Notes on water supply

Prepared by Masen
Chapter one
Introduction
1.1 Water supply, its objectives, immediate and long term impact
Water supply engineering is the branch of civil engineering that deals with the supply of safe
water for various purpose (e.g. Domestic, industrial, commercial and public supply) in sufficient
amount efficiently.
1.1.1 Objective of water supply
 To supply safe and wholesome water to the consumers: to protect public health from various
water born disease
 To supply water in adequate quantity to the consumers: Quantity of water should be sufficient
enough to fulfill water demand of the consumers.
 To make water easily available to consumers so as to encourage personal and household
cleanliness.
 To develop hygienic condition in the locality.
 To improve economic condition of the locality.

1.1.2 Immediate and long term impact

There are mainly two types of water impact
 Positive Impact
Positive impact means, water supply system leave positive sign in the society. It diverts
people to positive thing to developed their society and agriculture. It also develop standard
of the people. It is also classified as
 Immediate impact
o Save time to go and bring so that this time can be used for other productive work.
o Improves hygienic condition so that time and money expenses for medicine are saved.
o Safe, reliable, adequate and effective supply is gained.

 Long-term impact
o Increase socio-economic activities of individuals, family and then community
o Increase the living standard of the people
o Help in the economic growth of whole nation

 Negative Impact
o Reduce downstream water and effects on aquatic life.
o Decreases ground water table.
o Pollution due to decreased quantity of water at downstream.

1.2 Definition of potable, contaminated and wholesome water.

1.2.1 Potable water
Water fit for drinking purpose or safe enough to be consumed by humans or used with low
risk of immediate or long term harm is termed as potable water. Potable water is suitable for
drinking purpose having pleasant taste and useable for domestic purpose.

1.2.2 Contaminated water

That type of water which contains microorganisms, chemicals, industrial or other wastes or
sewage so that it is unsafe for its intended use is known as contaminated water .Water containing
pathogenic bacteria and others organic bodies’ harmful to human health. This water can cause
various diseases such as typhoid, fever etc.

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1.2.3 Polluted water
It is synonymous to contamination but is the result of contamination. This water contains
substances unfit and undesirable for public health or domestic purpose

1.2.4 Infected water contaminated with pathogenic organisms is called infected water

1.2.5 Wholesome water

That type of water which is chemically not pure, but doesn’t contain anything harmful to
human health is called wholesome water. Wholesome water is neither chemically pure nor
contain excess minerals harmful to human health but contains useful or beneficial to human
health.

Requirement of wholesome water:

1. It should be free from microorganisms, radioactive substance, dissolved gas, salts, heavy metals
etc.
2. It should be colorless and sparkling
3. It should be tasty, odor free and cool
4. It should be free excessive amount of minerals and organic matter
5. It should be free from toxic, chemicals such as Arsenic, lead, selenium, boron, cyanide etc.
6. It should not corrode pipes
7. It should have dissolved oxygen and free from carbonic acid so that it may remain fresh
8. It should not be contaminated and should not cause water – borne diseases.

1.3 Major components of water supply systems

Water supply engineering starts from the demand of water by a community. It may be gravity system,
pumping system or combined both. Whatever be the system all requires some sources. The consumer
receives the water obtained from the source after passing through a lot of components or devices. These
devices used to provide safe water to the consumer are called components of water supply engineering.
These are nothing but the group of components of water supply scheme.

Followings are the components of water supply

1.3.1 Source of water

Primary source of water is precipitation which joins to the earth in the form of rain, snow, hail,
etc. Rainfall is the most important source as it occurs is retained in surface depression, carried away
as surface runoff in natural channel in the form of stream or river and some portion percolates into
the ground further infiltrated to natural ground water reservoir. This portion of precipitation that
may be utilize for water supply as source of water is available partly at the ground surface and
partly below the ground surface.

1.3.2 Intake
An intake collects water from a source and feeds it to the transmission main. The
functioning of water supply scheme largely depends on the intake, its location and construction.
Hence, require great care during construction. The type of intake required in water scheme depends
on the types of water source.

1.3.3 Pump
Pump is a lifting device commonly required to lift water from source which is operated by
the help of energy. Avoiding the use of this device save the operation and maintenance cost of
scheme but is essential when area to be served is located at a higher elevation than the source

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1.3.4 Collection Chamber
If one source is not sufficient to fulfill the requirement of demand, then two or more source
is selected. Each source has own separate intake. There may be one or two pipeline from intake to
stand post. If two set of pipeline are used then the projects become costly. So to minimize the cost
of project collection chamber is used which receives the water from two or more source based on
capacity. Function of collection chamber
• Settle course material contained in river or spring water.
• Remove floating debris like leaves, branches etc. from water.
• Safely dispose of surplus water collected in excess of the pipe capacity.
• Allow free flow to avoid creation of break pressure in the spring.

1.3.5 Transmission mains

Water conveyance from the source to treatment plant is entertained by pipe as known as
transmission main. Water from these pipes is not given to consumers though generally pipe lay
over the ground. Design of transmission pipe is considered for average flow.

1.3.6 Interruption Chamber:

A chamber provided in the transmission main to break high pressure without a float valve to
prevent from bursting pipe due to excessive pressure is called interruption chamber. In an open
system, when the dynamic head in the pipe line exceeds 60m an interruption chamber may be
provide.

1.3.7 Treatment or purification works

Raw. water may contain various impurities. The purpose of water treatment is to remove
.those impurities which are objectionable either from taste and odor aspect or public health aspect.
The aim of water treatment is to produce and maintain water that is hygienically safe, aesthetically
attractive and palatable, in an economic manner.

1.3.8 Reservoir/Storage tank

Reservoir is used to reserve water. Depending on the purpose of use, it can be clear water
reservoir, balancing reservoir and service or distribution reservoir. Clear water reservoir is used
for storing treated water, balancing reservoir for equalization or to address fluctuation of demand
whereas service or distribution reservoir for equalizes the hourly fluctuations and stores the water
for break down reserve and fire reserve as for firefighting.

1.3.9 Control valves

These are essential appurtenances provided in the pipelines. There are various valves used for
different purposes like to control and regulate the flow of water, releasing valve, air relief valve,
wash out valves etc.

1.3.10 Distribution system

It is a pipe network laying to deliver water to the consumers premises from the distribution or
service reservoir. Distribution system is designed for the peak flow. The method of laying
distribution system is guided by the road network of the city.

1.3.11 Break pressure Chamber/Tank:

These are the tank or a chamber facilitated in the rural water supply distribution system to
overcome the failure by burst of pipes due to excessive pressure. The function of the BPT is
releasing high pressure into atmospheric pressure.
Points to be consider while locating BPC/BPT

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• In the distribution line whenever the static head exceed 60m even if pipe with a pressure rating
of 10kg/cm2 is used.
• Easily accessible
• Replacement of an air valve by BPC at high points, if the design permits.

1.3.12 Public stand post

These are the last component of water supply system from where consumes collect water to
meet their household demand in rural area. If people cannot afford private connections in rural
area and as of scattered houses in the area a stand post serves to 8 to I 0 households.
1.3.13 Pipe line
The pipe line transfer water from the source to the service area. Pipelines require high
investment outlay and hence careful consideration is necessary for its design. Pipes are
manufactured from various materials which come in different sizes and pressure rating. The choice
of pipes for a particular situation is governed by its availability, resistivity to corrosion and
mechanical damages and pressure limit. There are two types of pipe line

1.3.13.1 Transmission pipe line

A pipe that feeds water to storage tank continuously for 24hrs from a source is called
transmission main. It is design without considering any peak factor. Washout should be provided
at about 1.5 km interval.

1.3.13.2 Distribution pipe line

It is used to supply water to the consumer pipes of different diameters and lengths constitute
a distribution network. Distribution pipe sizes are determined by the top flow rate when the water
is supplied through the stand post.

1.4 Need of water supply engineering

H man can ·survive without food, shelter and clothes for several days but can’t without water.
Animals and plants can't without water. Air and water are the natural gift. Animals and plants can't
survive without water. Everywhere water is needed for various purposes as follows:
 Drinking and cooking
 Power generation and industrial processes
 Bathing and washing
 Watering of towns and gardens
 Heating and air conditioning system
 Street washing
 Fire fighting
 Recreation of swimming pools, fountain and cascades
 Industrial purposes
 Flushing

1.5 Water supp1y scheme: Urban and Rural

Typical schematic diagram of w/s scheme for urban area is shown in figure 1.1. The components
are collection works includes intake and pump, transmission main, purification works, reservoir
and distribution systems. Pump may be required in case of lifting due to elevated supply area
than the source. Water purification works may also optional as depends upon source water quality.

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The population density of Nepal in rural areas is low and houses are scattered but also
affordability of consumers for private connection is low so that in rural area water supply service is
provided by public taps. Typical schematic diagram of w/s scheme for hilly rural area is shown in
figure 1.2. In hilly rural area common source is spring and · generally water quality of spring is not
necessary to treat. Hence water treatment is not provided in hilly areas also power system is avoided.
Sometimes stream may be used in rural areas as source so sedimentation and filtration is used but
sedimentation may be omitted or auxiliary. Break pressure tank (BPT) also known as pressure
releasing tank is provided in distribution lines to prevent pipes from bursting due to excess pressure
as greater elevation difference in rural areas and for the same purpose interruption chamber (I C) is
provided in transmission mains.

In terai either tube well or dug well is used as source for rural
water supply system. Dug well may be used by private
households or small community where as tube wells are used by
big community. The water from the well is lifted to elevated
reservoir and provided to consumers through public tap stand.
Typical schematic diagram of w/s for terai is shown as in figure
1.3.

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Chapter Two
Water Source
Source of water means whereas water available for different purposes
These are the different source of water
 Rain water
 Surface water and
 Under ground water
Water obtained through
precipitation is retained in surface
depressions, carried away as
surface runoff in natural streams or
rivers and percolates into the
ground and joins the groundwater.
This portion of precipitation which
may be utilized for water supply
obtained partly at the ground
surface and partly below the
ground surface. Various sources of
water available for water supply
may be broadly classified into
following categories as shown in
figure.

2.1 Surface source: lake, streams/rivers and impounded reservoir. Capacity calculation of
impounded reservoir
Water available at the ground/earth surface is termed as surface source. The water quality
and quantity of surface source depends on rainfall patter; climatic and geological factors. Various
forms of surface sources of water are of the following.
 Lake and ponds
Lake: A large natural depression or hollow formed in earth's surface, which gets filled with
water is a lake. Lake is mostly found in mountainous region. The quantity of water available
in lake is generally very large, though it depends upon its size, catchment/drainage area, annual
rainfall, porosity of ground and geological formation. The quality of lake water mainly depends
upon the characteristics of the catchment. The water in a lake would be relatively of good
quality if it is located in the uninhabited upland hilly areas though high degree of treatment of
water may be required if lake is small and contain still water because that may have plenty of
algae, weed and other vegetation growth imparting bad smell, taste and color to the water.
Ponds:It is natural/artificial depression filled with water. Main source of water of pond is the
rainfall. It contains lots of impurities so it is not useful for water supply purpose. The quantity
of water in ponds is very less and used for washing purpose, animal bathing etc.

 Stream or rivers
Stream: A stream is a natural channel which carries surface runoff received by it from its small
catchment. The discharge in streams is much in rainy season than other seasons. Those streams
which dry up in summer and contain water only during rainfalls are known as rainy streams.
Streams may be perennial or non- perennial. Quality of water is good in high altitude except the
water from the first runoff but sometimes it contains impurities and can be used after some
treatment. It is natural channels which carry surface run-off
 found in mountainous region
 quantity of water is variable with season
 quality is generally good at its origin
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 quality deteriorates as it flows through the plain areas.(sand, silt, clay, organic matter etc.)
 can be used as a source by storing stream water during high flow period
 necessary to analyze the water quality before use
River: A river is a natural channel which carries surface runoff received by it from its catchment
or drainage area. River starts from hill when the discharge of large number of springs and streams
combine together. River water quality close to point of origin in the mountains is fairly good but
as the river approaches plains the quality of its water deteriorates considerably, because it picks
up lot of suspended matter, clay, silt etc. and becomes muddy in appearance so it always requires
treatment. '
 they are found in hilly region
 quantity of water is high
 quality of water is good at its origin but deteriorates as it travels towards the plain

There are two types of river:

(a) Perennial rivers (snow red rivers)
Perennial rivers are those in which water is available throughout the year. Such rivers are
fed by rains during the rainy season and by melting of snow during the summer season.
(b) Non perennial river/Intermittent rivers
Non-perennial rivers are those in which water is not available throughout the year. Those
ricers are available only during the rainy seasons.

 Storage/Impounded reservoirs:
An artificial and manmade storage reservoir or lake created by constructing
dam/bund/weir/bam age that flows in the river during high low period for use during the dry
weather or low flow period. The quality of water depends upon quality of river and stream and
needs to be properly analyzed and treated before supplying to the consumers.
There are two types of reservoir
(a) Single purpose reservoir:- used as only one purpose
(b) Multiple purpose:- used for more than one purposes such as water supply, irrigation,
hydropower
Construction of impounding reservoir is not feasible under the following conditions.
 When average annual flow in lower than average demand
 When rate of flow of river in dry season is more than that of demand.

2.2 Underground sources: springs wells and infiltration galleries

Water exist below the ground surface is termed as ground source. Ground water acquires its
chemical characteristics from surface water that percolates into the ground. The quality of
groundwater is generally good due to natural filtration as it percolates then infiltrate to deeper
strata. As ground water is not exposed to atmosphere it may be free from direct contamination and
pollution from runoff. Various forms of ground sources of water are of the following forms.
2.2.1 Spring
Sometimes ground water reappears at the ground surface in the form of springs. A spring is an
outflow of groundwater automatically to the ground surface due to geological formation. Springs
generally can supply small quantity of water, hence these can not be used as source of water for
big towns. Good developed spring can be used as water supply sources for small hill town

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2.2.1.2 Gravity Spring

These are formed when the underground water table gets exposed on the slopes of hills etc.
The water bearing stratum overlying an impervious stratum like rock or clay. The spring is formed
at the junction of these strata. It is shown in the figure.

2.2.1.3 Surface Spring

Created by a permeable water bearing layer overlying a impermeable (less permeable) layer
that intersects the ground surface. Water flows out from the weaker sports in the ground.

2.2.1.4 Artesian Spring

Ground water causes out under pressure created by water being stratum being under pressure
underlain and overlain by impervious strata. The rain water flowing on the surface enters into this
basin through the exposed portions on the top, flows down and is finally stored between the two
impervious layers under hydrostatic pressure. If hole is bored right up to this water bearing peculiar
shaped stratum, water rushes upwards sometime above the surface in the form of fountain, known
as artesian spring.

2.2.2 Wells
Water well is a vertical hole or shaft or shaft usually vertical, excavated in the ground for
bringing ground water to the surface. Types:
(i) Open well or Dug wells
(ii) Tube well
(iii) Artesian well

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2.2.2.1 Open Well

 top of the well is left open
 diameter of well is large
 constructed in brick, stone masonry, precast concrete rings
 diameter = 1 to 10m
 depth = 2 to 20m

2.2.2.1.1 Shallow Well

 Rests on the top water bearing strata and draw their supplies from surrounding material.
 Yield is not constant, varies with variation in water table
 Shallow wells constructed in series along the bank of river to collect the water seeping through
the banks of river.

2.2.2.1.2 Deep Well

 More than one water bearing layers are tapped in order to get more reliable supplies of water
 Quantity of water is more

2.2.2.1.3 Artesian Well

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These are ones in which the water rises, due to its pressure, above the level at which it is
encountered in the aquifer. These are caused when a previous stratum is enclosed between the two
impervious strata with the outcrop so high above the ground level.
This is usually formed in valley. When the boring is done, water comes out. No pumping is
necessary as far as the hydraulic gradient line lies above the top level of well. When it goes below the
top level of the well, pumping is necessary. The quality of water from artesian well is the same as that
of deep well water.

2.2.2.4 Tube well

 It is a long pipe sunk into the ground intersecting one or more than one aquifers or water bearing
strata.
 Diameter is much less (50mm to 200mm)
 Depth = 30 to 50mm
 In dry area, depth up to 300m is also found
Discharge = 40 to 50 l/sec and quality of water generally good, some minerals are found and
water is hard.

Confined and unconfined aquifers

An aquifer may be defined as a geological formation that contains sufficient permeable material
which permits storage as well as transmission of water through it under ordinary conditions. Terms
commonly used to represent an aquifer are groundwater reservoir and water bearing formation.
Confined aquifer :A confined aquifer is the one in which groundwater is confined under pressure
greater than atmospheric pressure by overlaying relatively impermeable strata. It is also known as
artesian or pressure aquifer.

Unconfined aquifer :An unconfined aquifer is one in which water table forms the upper surface of the
zone of saturation.

Aquiclude: An impermeable body of rock or stratum of sediment that acts as a barrier to the flow of
water. Clay layer is an example of aquiclude.

Aquifuge: An impermeable body of rock which contains no interconnected openings or interstices and
therefore neither absorbs nor transmits water. Example of aquifuge is granite bed.
Infiltration galleries
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It is a horizontal or nearly horizontal tunnel usually rectangular in cross-section and having
permeable boundaries so that water can infiltrate into the same. Ground water travel towards the river,
lakes, streams. This water which traveling can be intercepted by digging trench or constructing a tunnel
with holes on sides at right angles to the direction of flow of underground water

 Constructed Near The Bank Of A Perennial River.

 Depth 3 To 10m Below The Ground
 Discharge = 1500 to 7000 m3/day per 100m of gallery length
This underground tunnel is used for tapping underground water near river, lakes or streams are called
infiltration galleries. Sometimes these are also known as horizontal walls underground water may be
allowed to enter these infiltration galleries from both sides and one side as desired.
Infiltration galleries may be constructed with masonry or concrete with weep holes at 5cm x
10cm. Infiltration galleries are surrounded on side and top with gravel or pebble stone to increase their
intake capacity. Longitudinal slope is given to gallery.

2.3 Selection of water sources

The water source should selected considering various factors such as reliability, sustainable and safe,
free from water right problem, quality, quantity, location cost, etc. that will give adequate quantity ·of
water . with good quality require less treatment at affordable cost to consumers. The following factors
are generally considered while selecting a source of water supply for a particular town or city.
 Quantity of water: The source should be able to supply enough quantity of water to meet various
demand of city during the entire design period. Water availability in source may be fluctuating with
seasons so quantity of water that tapped in dry period should meet the water demand. Safe yield of
source should be adequate to meet desired demand of water throughout the year.

 Quality of water: The source should have safe wholesome, free from pollution of any kind and
other undesirable impurities. The impurities present in the water should be as less as possible and
these should be removed easily and cheaply.

 Location: Source of water should be located near to the community as far as possible and it should
be situated in elevated area. This will reduce length of pipe and water from the source would flow
by gravity and hence cost of project reduced. Pumping in system increase operation and maintenance
hence better to minimize the use as a component. If both ground and surface both source available
near the area to served obviously it is preferred to surface source because use of ground water may
has adverse impact in environment also lowering of water table may effects fertility of soil,

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subsidence of land etc. in case of use of ground source provision of ground water recharge may
require.

 Cost of water supply project: As far as possible overall cost of the w/s project should be minimized
so that water can be supplied to consumers at affordable price. Cost of water supply project mainly
depends on the location of source, elevation of source, water quality available in the source,
topography of the area, distance between source and community etc.

 Purpose to be used
 Sustainable and safe
 Reliable
 Non conflict among water user.

Surface water verses groundwater

Parameter Surface water Ground water
Understanding Easily seen & observed Invisible , mysterious, complex
Where found Stream, river, lakes etc. Everywhere beneath the surface in layers
of sand, gravel, clay or cracked rock, rarely
forms underground ‘streams’ , ‘lakes’
Uses Drinking water, food( fish, trapping Drinking water, energy, maintaining flow
rice etc.) transportation, bird/ animal in surface water courses
habitat, power, aesthetic and spiritual
health
Flow direction Downhill Usually from high elevation to low
elevation
Flow rate Fast Slow
Quantity Easy to assess. Supply problem rare Drilling and pumping,. Lots of water in
sand and gravel or heavily fractured rock.
Low yield in slit and clay or unfractured
rock
Quality Low dissolved( soft, low iron), high High dissolved(hard , high iron), low
organics, temperature changes, mud, organics, constant, cool temperature, no
clay, algae suspended solids
Consistency Changes with season Constant over time
Safety Variable bacteria/ virus counts Safe because of filtration and natural
purification process
Treatment Continuous chlorination Initial chlorination
Cost High low
Contamination Easily contaminated Not easily contaminated
risk
Contamination Natural breakdown by sun, air, mixing Clean-up difficult or impossible; may take
remediation etc. many decades

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Chapter three
Quantity of water
3.1 Water Demand and its variation
Water demand
Water is a prime necessity for life and that has led to growth of population along the banks
of natural water courses and springs. The water required for various purposes as domestic,
livestock, institutional and commercial, fire-fighting, industrial, municipal or public, losses or
wastage demand are the types of water demand. The amount of water required for a rural/urban
community depends on factors like the economic level of community, their consciousness and
other physical and social aspects. These various demand is not essential to take in account to
calculate total water demand of city or community or town so that fire-fighting, municipal,
industrial demand may be excluded in rural areas where as livestock demand is excluded in urban
area.
3.1.1 Domestic:
This includes the water which is required for use in private residence for drinking,
cooking, and bathing, washing of cloths, lawn watering and gardening and sanitary purpose. The
amount of domestic water demand depends on the living conditions of the consumers, · climatic
condition, habit, social status etc. The design of gravity flow community water supply schemes
in Nepal, in the past has taken 45 lpcd as per the recommendation of the WHO. The provision
of 45lpcd is considered to include allowances for drinking and cooking, personal washing,
wastage and leakage, and some portion of the domestic animal demands.
Generally adopted per capita domestic needs are as follows:-
COMMUNITY ADOPTED
S.N. REMARKS
POPULATION (lpcd)

1 <20000 45 Supply through public tap

2 <20000 70-100 Supply through private tap

3 20000 – 100000 100 – 150 Supply through private tap

4 >100000 150 - 200 Supply through private tap

3.1.2 Livestock:
The quantity of water required for domestic animals is called livestock demand.
Livestock is an important component of the life style in rural Nepal. It has utilizes both as draft
animals for tilling land and a source of income. The water consumption by the livestock
(animals) must be known specially for farms and livestock areas. The approximate consumption
given below:-
Big animal (Cowl buffalo/horse) 45 lit/animal
Small animal(Goat, dog, rabbit etc.) 20 lit/animal
Poultry (Birds, chicken, duck etc.) 0.2 lit/birds

3.1.3 Commercial /Institutional demand: It includes the demand for commercial establishments and
institutions like universities, school, cinema hall, office building, warehouse, stores, hotels,
hospitals theaters, clubs etc. Institutional demand refers to the water needed for offices, schools
and health posts, in the community. In some case, tourist resorts, local industries may also have
to be supplied water from the scheme. Government institutions deriving service from the water
scheme must also support the water user committee (WUC) in operating and maintenance the
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schemes. In community water supply scheme priority should be given to supply water to schools
and health posts. The following institutional water demand should be adopted:-

TYPES OF
S.N. DEMAND REMARKS
INSTITUTIONS

10 lit/student Day school

1 School
65 lit/students Boarders

1000 lit/day Without sanitation

2 Health post
3000 lit/day With sanitation

500 liter/bed/day With bed

3 Hospitals
2500 liter/hospital/day Without bed

200 lit/bed/day With bed

4 Hotel
500-1000 lit/day Without bed

5 Restaurant/tea stall/office 500-1000 lit/day

3.1.4 Public/Municipal demand

Water required for public or municipal utility such as washing and sprinkling on road,
flushing sewers, watering public parks etc. is municipal or public demand. A provision of 5 to
10% of the total demand is taken as this demand. This demand is only considered in urban water
supply system.

3.1.5 Industrial demand

Industrial area could be located far from the city though it may locate in periphery of city
which may be vital in calculating water demand. Normally 20-25% of total demand is taken for
industrial demand. It is considered only in urban area and depends upon the type and size of
industry.

3.1.6 Fire fighting demand

Fire is generally break in thickly populated localities and the industrial area and causes
serious damages of properties. During outbreak of fire, the water is used for firefighting is called
fire demand. This demand is not fixed so it is difficult to calculate demand. Different empirical
formula can be used to determine fire demand but it cannot directly used for Nepalese context.
This demand is considered in urban water supply system.
The quantity of water required for fire fighting is calculated by following formula
If Q= water required in l/min and P= population in thousands then.
(a) According to National board of fire
Q = 4637 P (1-0.01 P )
Where Q=quantity in lit/sec
P = population in thousands

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(b) According to Freeman’s formula

Q = 1136.50(P/5 + 10)
Where Q=quantity in lit/sec
P = population in thousands

(c) Kuichling’s formula,

Q = 3182 P
Where Q=quantity in lit/sec
P = population in thousands

(c) Buston’s formula

Q = 5663 P
Where Q=quantity in lit/sec
P = population in thousands

(d) Indian water supply manual (1976) formula:

Q = 100 P where Q in m3/day
Where Q=quantity in lit/sec
P = population in thousands

3.1.7 Loss and wastage: Loss and wastage may be termed as unaccounted for water which includes
water due to faulty valves and fittings, poor distribution system, defective pipes, unauthorized
connections, tap open etc. Lost and wasted being uncertain it cannot be predicted precisely so
generally it is taken as 15 to 20% of total demand.

Causes of loose and wastage of water.

 Leakage and over flow reservoir.
 Leakage from main and service pipe connections.
 Leakage and looses from consumers premises.
 Wastage for public taps.

3.1.8 Total water demand

The sum of all water demands is total water demand as given below.
TD=DD+LD+ID+ID+PD+FD+LD
Where,
TD = Total water demand
DD = Domestic water demand
LD = livestock demand
ID = institutional and commercial demand
ID = Industrial demand
PD = Public/municipal demand
FD = fire demand
LD = Losses and wastage demand

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3.1.9 Per capita demand
It represents the average consumption or demand of water per day for various purposes including
all demand of water for person. It is expressed as Lpcd/Lphd.
Let 'Q' be the total quantity of water required per year in liters by city or town having population
(P), and per capita demand or rate of water demand (q) usually expressed in lpcd is given by the
following expression.
𝑄
Average rate of demand (q) = (𝑃𝑥365) lpcd

Water demand variation.

The rate of demand of water represents the average consumption or demand of water per
capita/head per day. Rate of demand does not remain constant but varies with the season or month of
the year, with the days of week, and with the hours of the day. These variations in the rate of demand of
water are termed as,
i) Seasonal variations
The rate of demand of water varies considerably from season to season. In summer water
demands usually 30 to 40% above the annual average rate of flow of water, because more water is
required for drinking, bathing, washing etc. In winter the average rate of demand is about 20% lower
than the annual average rate of demand of water because of less requirement of water.
Qseasonal = 1.3 X Qaverage (In India)
Qseasonal = 1 X Qaverage (In Nepal)

ii) Daily variations

Due to change in the day to day climatic conditions, or due to the day being a holiday or some
festivals day the rate of demand of water varies from day to day and called daily variations.
Qdaily = 1.8 X Qaverage (In India)
Qdaily = 1 X· Qaverage (In Nepal)

iii) Hourly variations

Maximum demand of
water usually occurs in
the morning and in the
early morning hours the
demand of water is at its
maximum and also during
noon. Hence, demand
also varies even hour to
hour called hourly
variation. A typical graph
showing hourly variation
in the rate of demand is
shown in figure 3-2.
QHourly = 1.5 X Qaverage
(In India)
QHourly = 2 to 4 X Qaverage
(In urban area of Nepal)
QHourly = 3 X Qaverage (In
rural area of Nepal)

3.2 Definition of design

period
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A water supply project is planned to meet the present demand of the city or town as well as the
demand for a reasonable future period or number of years is considered is called as design period. Any
water supply project is planned to meet the present requirements of community as well as the
requirement for a reasonable future period(up to service year) taken in design.
Design period = Design year - Base year

It is taken as 22 to 30 years and even for 50 years if dam storage is done. In Nepal this period is
generally taken as 15 -20 years in rural areas and 25 – 30 ( generally 25) years in urban areas. It should
be realistic i.e. neither long (financial overburden) nor short (uneconomical).
The Selection Basis Of The Design Period are as follows.

 Availability of funds: If only limited fund is available then a shorter design period will have to be
considered and vice-versa.

 Availability of water: Design period is controlled by the water available in source so that water
should be sufficiently available for that design period.

 Population growth rate: Growth of population is a major factor that of area to be served in fixing
design period. In our context Nepal design period of rural water supply project is fixed as per
population growth rate i.e. if higher the growth rate less design period and vice-versa.
r≥ 2, design period is 15 yrs.
r≤, design period is 20 yrs
 Economic development: Economic development of the area to be served is also a factor which
governs to select design period. If economic development is rapid design period considered should
be less.

 Life of the pipes and construction materials: Design period should not be greater than components
useful life.

 Rate of interest of loan: If more the rate of interest lesser will be the design period and vice-versa.

Typical design periods

Usually in rural areas 15 to 20 years is taken as typical design period where as up to 30 years is taken as
a typical design period in urban areas as shown in figure 3-1.

Survey year
This is the year in which data are collected for a start of the project of supplying water.

Base period
A water supply project takes· time to conduct survey, analysis, design and construction of the
components of water supply system. The time required for survey, design and construction before
implementation is called base period. Base period is generally taken as 2 to 3 years but it is taken as 2
years in Nepal.

Base year

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This is the year in which water 1s actually supplied to the consumers (implementation).

Design year
This the year considered for which water supply system is designed i.e. service of the water supply
system can fulfill required demand. Rehabilitation or strengthening of the components may be required
to get service from the project after design year.
Design Year = Survey Year + Base Period + Design Period

Design year = (Survey year + Base period) + Design period = Base year + Design period

3.3 Population forecast & Population forecasting method

Population forecast:
After fixing the design period it is necessary to forecast or estimate the future population for the
end of service year as it fluctuates due to the deaths, births and migrations. Normally population
increases and the increment of the population of the city depends upon various factors such as living
standard, economic factor, social facilities industrial potential, infrastructure development,
opportunities, climates etc.

Factor effecting Population Growth

Following are the factors that effect the population growth that is
a) Economic factor Development program
b) Social facilities
c) Communication and information
d) Tourism
e) Community life
Design year = (Survey year + Base period) + Design period = Base year + Design period
Population forecasting method:
3.3.1 Mathematical method: Arithmetical, geometric/increment increase, decrease rate of
growth
3.3.1.1 Arithmetical
According to this method population is increasing decade to decade at a constant rate. The rate
of population with time is constant. This constant rate of increase in population in future is taken as the
average increase in population per decade during a number of past successive decades.
Pn = Po+n.I
Where, Pn = future population
Po = present population
n = no of decade
I = average rate of increment per year = (A1+A2+A3+A4+A5)/5

3.3.1.2 Geometric
According to this method, increase in population from decade to decade remains constant. If
Ig = average percentage per decade,
rg = increase per decade expressed as ratio (Ig/100) , then the population at the end of n decade will be
Ig
Pn = Po (1+ )n
100
= Po (1+rg) n
 gives the highest value
 suitable for cities growing rapidly

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3.3.1.3 Increment Increase
According to this method, the average increase in the population is determined by the arithmetical
method and to this is added the average of the net incremental increase once for each future decade.
n(n  1)r
Pn  Po  nI 
2

3.3.1.4 Decrease rate of growth

Assumed that city has some saturation population after that population growth rate decreases as the size
of city increases. According to this method, rate increase of population never remains constant but varies
between the population P and the time T for a developing city. The population of a city will grow until
it reaches a saturation population which is established by limit of economic opportunity. All populations
thus grow according to the logistic or S-curve.
Pn = Po+(Ps-Po)(1-e-10kn)
Where, Ps = saturation population of city
k = a constant
Po = latest known population (base year)
2 PoP1P 2  P12 ( Po  P 2)
Ps =
( PoP 2  P12 )

P1 = Population t1 decrease prior to the latest

known Population(Po)
P2 = Population t1 decrease prior to the latest known Population(P1) or 2t1 decades prior
to latest known population Po
1 𝑃𝑠 − 𝑃𝑜
𝐾= 𝑙𝑜𝑔𝑒 ( )
10𝑡 𝑃𝑠 − 𝑃2

3.3.2 Graphical method- extension and comparison

3.3.2.1 Extension
According to this
method a curve is drawn
between the population P
and time T, with the help
of census data of
previous few decades, P
so that the shape of the
population curve is
obtained up to the
present period. Then
curve is then carefully
extended from the
present to future decades.
For the extended part of
the curve, the population
at the end of any future
decade is approximately determined

3.3.2.2 Comparison
It assumes that the city under consideration will develop as similar cities developed in the
past. The method consists of plotting curves of cities that, one or more decades ago, had P the
present population of the city under consideration. Future population of a city under

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consideration is predicted comparing the census data of similar cities which have reached the
present population of the city under consideration some year earlier.

3.3 Factors affecting demand of water

Following are the factor which effect the demand of water

 Climatic condition
 Size and type of community
 Living standard of people
 Quality of water supply
 Industrial and commercial activities
 Pressure in distribution system
 System of supply (continuous or intermittent)
 Sewage facility or sewerage systems
 Metering or non metering system
 Water rates or cost of water
 Customs and habits of inhabitants
 percentage of area of gardens and lawns

Numerical Example:
Compute the fire demand of a city having population of 140000 using various formulae.
Solution:
Population in thousands (P) = 140
We know that, according
1. Kuiching’s formula
Q = 3182 P  3182 140 = 37650 liters/min = 0.627 cumecs
2. Buston’s Formula
Q = 5663 P  5663 140 = 67000 liters/min = 1.117 cumecs
3. Freeman’s formula
P   140 
Q = 1136   10   1136   10  = 43168 liters/min = 0.719 cumescs
5   5 
Number of fire streams,
F  2.8 P  2.8 140 = 33 approximate

4. National Board of Fire Underwriter’s formula

Q = 4637 P (1  0.01 P )  4637 140 (1  0.01 140 ) = 48,374 liters/min
= 0.806 cumecs

5. Indian water supply manual(1976) formula

Q= 100 P  100 140  1183 .22 liters/min

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Chapter four
Quality of water
Quality of water is the degree of goodness of characteristics (physical, biological and chemical) of
water in all aspects. In the formation of water drop initially. It may be pure after mixing dissolved gasses,
suspended colloidal and dissolved substances. It may be polluted. The polluted water is harmful to
human health. Followings are the properties of good water for domestic use
 It should be reasonably soft
 It should be cheap.
 It should be free from bacteria, algae and other living organism and objectionable dissolved gasses.
 It should be colorless, odorless and tasteless.
 It should be free from excessive amount of salts and organic matter.
 It should be free from suspended colloidal and dieses impurities.

4.1 Impurities in water ,their classification and effects

4.1.1 Based on the water quality Analysis Parameter
Various impurities may be present in water which is classified by two methods as follows.
 Classification on the basis of properties or characteristics of impurities
a. Physical impurities
Those impurities which affect the physical characteristics of water such as color, odor, taste and
turbidity. e.g. Sand, silt, mud found in suspension or in colloidal stage in water.

b. Chemical impurities
Chemical substances present in water affect the chemical characteristics of water such as pH,
solids, salts of minerals, hardness, alkalinity, chloride, nitrogen etc. They may be organic or inorganic.

c. Biological impurities
Presence of the bacteriological impunt1es . affects the bacteriological characteristics of water
such as pathogenic (Salmonella), non-pathogenic (E-coli) microorganisms. Bacteriological impurities
present in water causes diseases to humans.

4.1.2 Based on the size of the substance/state of presence

a. Suspended impurities
Dispensing of solid particle in water that are large enough to be removed by sedimentation and filtration.
 Size of dia>10-6m = 1micron
 Microscopic in nature and can be seen by naked eye
 Organic impurities such as Algae, Fungi , organic maters & Inorganic impurities such as clay,
silt, sand.
 Measured in NTU, STU
Effects
 Cause turbidity or murkiness in water
Remove method
 Can be removed by filtration surface and heavier one settle down

b. Dissolve impurities
Water is a very good solvent and can dissolve all the salts to which it comes in contact. The dissolved
impurities may contain organic compounds inorganic salts, liquid or gases.
 Impurities which remains in dissolved state
 Minerals may remain in dissolved state types organic compound, inorganic salts and minerals
 Exposed in terms of TDC (total dissolved solids)
 Units mg/lt or ppm
 Size <10-3m
Effects:
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 Salt of calcium and magnesium in water causes bad taste, hardness, alkalinity etc.
 Iron oxide and manganese when dissolved cause odor, taste, red or black or brown color,
produce stain's on cloth in laundries and plumbing fixtures in buildings.
 Gases likes 0 2 and C02 causes corrosiveness and H2S causes smell or rotten egg.
Remove method:
 Dissolved impurities is in liquid having only one phase so such impurities can be remove ·.
only by phase change such as precipitation, adsorption, distillation.

c. Colloidal impurities
These impurities are so small that these carmot be removed by ordinary filter and are not visible
to our necked eyes. It can not be filtered and doesn’t settle down. The size of colloidal 1 micron to 1
milimicron
 Very fine divided dispersion of particles.
 Size 10-9m to 10-6m.
 Difficult to settle in tank.
 Imparts color to water.
 They carry electrical change.
 Sources of epidemic.
 Measured by color test.
Type Cause Effects
Bacteria Some cause disease
Suspended Impurities Algea and protozoa color, order, taste and turbidity
Clay and silt Turbidity

Bicarbonate hardness and alkalinity

Carbonate hardness and alkalinity
sulphate hardness
chloride hardness
b) salt of sodium
Bicarbonate softening and alkalinity
Carbonate softening and alkalinity
sulphate dental fluorosis or molted enamel
chloride taste
c) Metals and compounds
Iron Oxide Taste, red color, hardness and corrosiveness
Dissolved (Impurities) salts of
Manganese Black and brown color
calcium and magnesium
Lead cumulative poisoning
Arsenic Toxicity
Barium Toxic effect on heart and nerves
Cadmium toxic and illness
cyanide Fatal
Boron Affects central nervous system
Selenium Highly toxic to animals and fish
silver Discoloration of skin
Nitrate Blue baby disease
d) Gases
Oxygen Corrosiveness
Carbon dioxide acidity and corrosiveness

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Hydrogen sulphide strong odor acidity, corrosiveness
Vegetable color, taste acidity
Suspended organics impurities
animal(dead) Harmful disease germs and alkalinity
Vegetable produce bacteria
Dissolved organic impurities animal(dead) pollution of water and disease germs

4.2 Hardness of water, types of hardness, Alkalinity in waters

a. Hardness of water
Hardness is that characteristic of water which prevents the formation of sufficient lather or foam
with soap. The hardness of water is caused by presence of bicarbonates, sulphates, chlorides and.
nitrates of calcium and magnesium. The excess amount of hardness in water may be unfit for use of
water because it interferes during use of soap, in boilers, in dyeing industry by modifying color, life
of pipe due to corrosion, taste of food etc.

Types of hardness
Temporary hardness
It happens due to presence of carbonate and bicarbonates salts of calcium and magnesium. It is
removed boiling or mixing the lime in water. Its also known as Carbonate hardness.
Ca(HCO3)2 → CaCO3 + H2O + CO2
Mg(HCO3)2 → MgCO3 + H2O+ CO2

Permanent hardness
They are caused by sulphates and chlorides of Calcium and magnesium . It is also known as Non
carbonate Hardness. It can’t be removed by simple process. It can be removed by special methods
of water softening (permit process or ion exchange process). Hardness is expressed in terms of
equivalent amount of CaCo3 as:
eq .wt of caco
Hardness due to M++ as CaCo3, =hardness as M++ (mg/lit) X eq et.of M++3
Total hardness (TH) = Temporary hardness + Perm hardness
= Carbonate hardness (CH) + Non carbonate hardness (NCH)

T.H. = CH + NCH
Acceptable range <250 mg/lit

Effect of hardness:
 Causes more consumption of soap
 Can affect working of dyeing system
 Provides scales and boilers
 Causes corrosion and incrustation in pipes
 It makes food tasteless
 Increase soap consumption
 Reduce the efficiency of filtration due to the formation of scale

b. Alkalinity in waters
Alkalinity is caused by hydroxides, carbonates and bicarbonates but most natural alkalinity is due
to bicarbonates. Alkalinity caused by hydroxides is called hydroxide alkalinity or caustic alkalinity,
caused by carbonate is Carbonate alkalinity and caused by bicarbonate is called bicarbonate
alkalinity. Some but not all the compounds causing alkalinity also causes hardness. Bicarbonate
alkalinity is chief form of alkalinity so that it formed in considerable amount from the action of
carbon dioxide upon the basic material in the soil. Normally carbonate and hydroxide alkalinities
may be present with bicarbonate alkalinity or hydroxide alkalinity. These bicarbonate and hydroxide
alkalinity do not exist together in W!\ter. So, total alkalinity (TA) is sum of
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carbonate alkalinity (CA) and bicarbonate alkalinity (BCA).
𝑒𝑞.𝑤𝑡.𝑜𝑓 𝑐𝑎𝑐𝑜3
Alkalinity due to B. as CaC03 = alkalinity as B- X
𝑒𝑞.𝑤𝑡 𝑜𝑓 𝐵 −

Alkalinity as C03 in (mg/lit) = CA in mg/lit

Alkalinity as HC03-= BA in mg/lit
Total alkalinity (A) =BA+CA

Relation between hardness and alkalinity

If total hardness (TH) is greater than total alkalinity (TA), then carbonate hardness (CH) is equal to
total alkalinity (TA) and non carbonate hardness (NCH) is equal to total hardness minus carbonate
hardness as given by following expression;
If, TH> TA
then, CH=TA
NCH =TH-CH=TH-TA
If total hardness (TH) is less or equal to total alkalinity (TA), then carbonate hardness (CH) is equal
to total alkalinity (TA) and non carbonate hardness (NCH) is equal to zero as given by following
expression:
If, TH ≤ TA
then, CH=TH
NCH=O [1 ppm = 1 mg/lit]

4.3 Living organism in water: virus, algae, worms and bacteria

The water available at the source may contain various types of living organisms. Some of the
organisms are water borne and remain in water due to their natural habit. Some organism introduced in
water bodies by man during disposal of sewage. Some of the living organisms such as bacteria, viruses
and protozoa are infectious to human and are responsible for the serious outbreak of fatal water-borne
diseases. The following are the main living organism of water:

4.3.1 Virus
It is defined as a group of infections agents which are smaller than ordinary bacteria.
These are the smallest biological structures known to contain all the genetic information
necessary for their own reproduction. Water borne viral pathogens are known to cause:
Polio : It causes poliomyelitis to children.
Coxsackie : It affects our throat i.e. in breathing.
Hepatitis : It causes a type of jandis.
Echo : it causes meningitis, diarrhea
(Enteric Cytopathogenic Human Orphan)
It can be inactivated by treating water with chlorine, about 0.4 mg/lit of free available
residual chlorine with a contact period of 30 minute is sufficient to inactivate infectious hepatitis
virus.

4.3.2 Algae:
These are small chlorophyll bearing single called plant life which lives in presence of
sun-light. They consume mineral matters CO2 and nitrogenous compounds as their food and
liberate oxygen. It causes no human disease. They cause turbidity and apparent color in water.
They, sometimes, cause trouble by clogging filters. . It can be controlled by covering the tanks
so as to exclude sun light or by copper sulphate solution.

4.3.3 Worms/Helminthes
The life cycles of worms often involve two or more animal hosts, one of which can be
human and water contamination may result from human or animal waste that contains worms.
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These are microscopic as well as macroscopic and can enter directly to the human body through
skin or on drinking of water. They may be parasitic as well as free living. Hook worms, tape
worm etc. are parasite. They are classified as:
a) Nematodes or round worms
b) Rotifers
c) Flat worm
i) Tape worms (Certodes)
ii) Flukes (Trematodes)
Worms cause schistosomiasis
4.3.4 Bacteria:
Bacteria are single-cell microorganisms, usually colorless, and are the lowest form of life
capable of synthesizing protoplasm from the surrounding environment. They are . prokaryotic,
unicellular, and either free-living in soil or water or parasites of plants or animals. The bacteria
usually found in water range from I to 4 microns in length. Reproduction of bacteria is normally
by cell division of fusion. The original cell divides into two equal parts and each part of the cell
develops to full size bacteria. Almost bacteria get developed in the intestine of 'warm-blooded
animal. These come out through the excreta.

4.4 Water born diseases: water-borne, water-washed, water-based, water-vector, etc.

4.4.1 Water borne
Disease due to consumption of water containing impurities is called water borne' disease.
Waterborne diseases are caused by pathogenic microorganisms that most commonly are
transmitted through contaminated water. Water borne disease is also known as water quality
disease. This is due to; presence of chemicals e.g. iron, lead, arsenic etc. and presence of
microorganism like bacteria, virus, worms etc. potentially water borne disease include the
classical infections, notably.e.g Cholera(caused by vibrio comma ), Typhoid fever:
(Transformed by means of bacteria 'Salmonell,Diarrhea, Dysentery

4.4.2 Water washed

For the transmission of these diseases we need not necessarily to drink water. It gate
transmitted due to lack of cleanness, poor sanitation and education. It depends on the quantity of
water.E.g. Trachoma, scabies, fungal infection of skin.

4.4.3 Water based

A water based disease is that type of disease in which the pathogen has spent same part of
life cycle in a water snail or aquatic animals. These diseases are .also known as water contact
disease. All these disease are due to infection by parasitic worms (helminthes) which depend on
aquatic intermediate hosts to complete their life cycles.eg. all disease related with infection from
parasitic worms. other disease acquired by eating of in sufficiently cooked fish, crabs, crayfish or
aquatic vegetation.

4.4.4 Water – vector

Water vector diseases spread by insects which either breed in water or bite near water. The
transmission of these disease is complex so that it involve at least three living things; a host, a
parasite and a carrier or vector (insect, fly or mosquito). These diseases are also known as water
site insect carried diseases. Malaria, yellow fever, dengue, onchocerciasis (river blindness) are
example of water vector disease.

4.5 Physical, chemical and biological analysis of water: tests for temperature, color, odor, taste,
turbidity, pH; solids, MPN chloroform etc.
Water analysis

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The examination of water is also known as water analysis which is done in systematic manure
to identify the water quality or the presence of impurities in water. The water analysis or examination
is conducted for the various purposes as listed below.
 to ascertain the quality of water & quantity of various impurities.
 to verify the treated water quality is as per standard or not.
 to identify the dose of chlorine, coagulant etc. in treatment plants
 to prescribe the degree of treatment for the required water quality

4.5.0 Physical
4.5.0.1 Temperature
Temperature of water has an effect on the physical properties of water such as density, viscosity,
surface tension, saturation value of gases dissolved in water, biological activity. Temperature of water
is determined by ordinary thermometers. For public water supply it should be between 10 °C to 15.6
°C. Temperature greater than 25 °C is undesirable and above 35 °C unfit for public water supply.

4.5.0.2 Color
Pure water is colorless, but water in nature is often closed by foreign substance. It is measured by
the ability of the solution to absorb light. It is measured by tintometer. The intensity of color is
measured on platinum – cobalt scale. 1 mg of platinum plus ½ mg of metallic cobalt dissolved in 1
liter of distilled water is one true color unit. For drinking water color should not be greater than 5 ppm
in platinum cobalt scale. Greater than 5 is tolerable but rejected greater than' that 25 ppm in platinum
cobalt scale.
1 platinum cobalt scale= 1 ppm= 1 mg/lit

4.5.0.3 Turbidity
Turbidity is measure of the extent to which .Light is either absorbed or scattered by suspended
material in water. Absorption and scattering are influenced by both size and surface characteristics of
the suspended material. It is measured on silica scale which is defined as the turbidity produced by 1
mg of silica in 1 lit of water is 1 unit. The original measuring apparatus called a jakson turbidity meter,
was based on light absorption and employed a long tube and standardized candle. The glass tube was
calibrated with readings ·one JTU being equal to the turbidity produced by 1 mg Sio 2, in 1 liter of
distilled water. Turbidity of 5 ppm is accepted and rejected if it is greater than 10NTU.

4.5.0.4 Taste and Odour

No objectionable taste should be present in water. The intensities of the odors are measured in
terms of threshold number. For water supply it should not be more than 3. Testing of water is done 1st
at 200C then at 180C. Threshold number is nothing but reciprocal of the ratio of dilution with odor free
water required to reduce the odor to a point that is just detectable.

4.5.1Chemical
The chemical examination of water involves the tests which are undertaken to determine the
chemical impurities and the corresponding chemical characteristics of water.

4.5.1.1 Total solids

The solids present in water may be either dissolved or suspended solids and sum of these
suspended and dissolved solids is total solids. The solids present in water is generally expressed in
ppm or mg/lit.
Up to 500 ppm and should never exceed 1000ppm

4.4.1.2 PH value

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PH value may be defined as the logarithm of the reciprocal of hydrogen ion concentration. The
product of OH- and H+ is 10-14 for pure water.
If PH<7 water is acidic
If PH= 7water is neutral.
If PH>7 water is alkaline.
It is determined by electrometric and colorimetric method. The value of pH drinking water as per
National drinking water quality standards (NDWQS) of Nepal is 6.5 to 8.5.

4.5.2 Bacteriological analysis of water

a) Total count or agar plate count test: It is also known as standard plate count. In this method 1 ml of
water sample is diluted in 99 m1 of sterilized/distilled water and diluted 1 ml water is mixed with 10 ml of
agar gelatin (a culture medium used to cultivate bacteria) and incubated at 3 7 °C for 24 hrs. or 48 hrs. at 20
°C. The bacterial colonies which are formed, are then counted and the results are computed per 100 ml. For
drinking water the total count should not exceed 1 per 100 ml.

b) Multiple tube fermentation technique/E-coli test: This test is divided into the following these parts;
i) Presumptive test
The presumptive test is based on the ability of coliform group to ferment the lactose broth ·and
producing gas.
Procedure:
(1) Definite amount of diluted samples of water are taken in multiples of 10, such as 0.1 ml, 1.0 ml, I 0 ml
etc.
(2) The water sample is placed in . standard fermentation tubes containing lactose broth
which is incubated at temperature of 3 7 °C for a period of 48 hrs.
If gas is seen in the tube after this period, it indicates the presence of E-coli group and result of test is positive.
If no gas is seen, it indicates the absence of E-coli group and the result of text is treated as -ve.

ii) Conformed test

The conformed test consists of growing cultures of coliform bacteria as media which
suppress the growth of other organism. The gas produced in presumptive test does not conform the
presence of bacteria of coliform group because these may be other bacteria present which also ferment
lactose. So a portion of water from presumptive test is taken and placed in another fermentation tube
containing brilliant green lactose bile as culture medium. It is again kept in incubator at 3 7 °C for 48
hrs., the evolution of gas in these tubes would conform the presence of the organisms of the coliform
group and vice-versa. Colonies of bacteria indicates the presence of E-coli and completed test is
necessary.

iii) Completed test

This test is based on the ability of the culture grown in the conformed test to again ferment the
lactose broth. Colonies of bacteria grown in conformed test are kept into lactose broth fermentation
tubes and agar tubes. The tubes are kept for incubation at 3 7 °C for 24 hrs. to 48 hrs. If gas seen in
tubes, it indicates the presence of E-coli group and the result of the test is treated as positive and further
detailed tests are carried out to detect the type of bacteria present in water. Again the absence of gas
indicates negative result and water is safe for drinking.

c) Membrane filter technique

The bacteria present in water are retained on the membrane having microscopic pores. The membrane
with the bacteria is then put in contact with a suitable nutrient (M-Endo's medium) which inhabits the
growth of bacteria other than the coliform group. It is than placed in an incubator at 3 7 °C for a period
of 20 hrs. The bacteria of coliform group if present in water are developed into visible colonies which
can be counted with the help of microscope.
colony counted
coliform colony/100ml = 𝑋100
ml of sample

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Most probable number index or MPN

MPN is defined as bacterial density which is based on the laws of probabilities and statistics and hence
it provides a more rational approach for indicating the concentration of E-coli in water from the multiple
tube fermentation technique.
I OOx nos.of positive test tubes
MPN per I 00 ml of sample=
√ml in all portions x ml in negative portions
Example

4.6 Water quality standard, WHO standard and Nepal standard for domestic use
Water available in source may contain many harmful constituents i.e. various impurities at
various concentrations. Presence of higher concentration of impurities in drinking water cause disease
but · presence of some minerals in water may be beneficial to human beings which should be within a
limit. The maximum concentration limit of impurities in water at which it is not harmful to human health
is termed as water quality standards. Water analysis means to determine the various impurities
present in the water. Treatment plant is designed based on their impurities. Analysis of water has to
perform before designing treatment plants, after the treatment supply to the public. Daily and seasonal
variation in water qualities necessaries water analysis frequency and over a long period of time.

4.6.1 Purpose of water analysis

 To determine the level of organic impurities.
 To determine the presence and absence of an excess of any particular constituents affecting
drinking quality.
 To classify the water with respect to general level of mineral constituents.
 To determine the degree of clarity and aeration the nature of matters in suspension.
 To set out line of purification process and specially various stage I it.
 To determine chemical and bacteriological population of water.
 To ascertain weather purification of water reached the required standard.

4.6.2 Water sampling and storing

The collection process of water for its physical, chemical and other examination is called water
sampling. Before testing the samples are collected from the sources of water should be done in proper
manner so that it is true representatives and small volume to be transportation the lab.

Following points to be consider while collecting sample

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 If water is collected from a tap, sufficient quantity of water should be allowed to pass through the
tap before collecting sample from it .
 If water is collected from surface stream or river, it should be collected about 40 – 50cm below
the water to avoid surface impurities.
 If water is collected from the ground surface i.e. well, tube well etc. sufficient quantity of water
should be pumped out before collecting the sample.
 For the physical examination of water can be collected on fully cleaned bucket or bottle or jar but
chemical examination water sample is collected 2 lit on the cleaned bottle.

4.6 Water quality standard, WHO standard for domestic use.

WATER QUALITY WHO GUIDE NEPAL
S.N.
PARAMETER LINE GUIDE LINE
1 Turbidity, NTU 5000 5
2 Color, TCU 15 15
3 Taste Unobjectionable Unobjectionable
4 Odour Unobjectionable Unobjectionable
5 PH 6.5 - 8.5 6.5 - 8.5
6 Iron , mg/lt 0.3 0.3
7 Maganese, mg/lt 0.1 0.2
8 Total Hardness as CaCO3, mg/lt 0 500
9 Amonia, mg/lt 0 1.5
10 Disolved Solids, mg/lt 500 500
11 Nitrate, mg/lt 50 50
12 Chloride, mg/lt 250 250
13 Free Chlorine, mg/lt 0.2 - 0.6 0.2 - 0.5
14 Arsenic, mg/lt 0.01 0.05
15 Aluminum, mg/lt 0 0.2
16 Lead, mg/lt 0.01 0.05
17 Cadmium, mg/lt 0.3 0.3
18 Boron, mg/lt 0.3 0.3
19 Chromium, mg/lt 0.05 0.05
20 Nickel, mg/lt 0.02 0.02
21 Hydrogen Sulphide, mg/lt 0.05 0.1
22 Sodium, mg/lt 200 200
23 Copper, mg/lt 1 1
24 Fluoride, mg/lt 1.5 1.5
25 Zinc, mg/lt 3 3
26 Mercury 0.001 0.001
27 E - Coli Nil Nil

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Chapter five
Intake works
Intake is a device or a structure installed in the water source to permit the withdrawal of water
and discharge it into an intake conduct then to the treatment plant. It consists of openings, grating or
strainers, valve, operating devices, pump, a structure or housing to support intake conduct, an intake
conduct etc. The main function of the intakes works is to collect water from the water source and then
discharge water so collected, by means of pumps or directly to the treatment plant. The basic function
of intake are:
• to ensure required water
• to reduce sediment entry
• to check trash and debris entry along with water entering
• to prevent entry of ice
• to secure entry of water with minimum disturbance

5.1 Site selection for intake

 Location of intake site should be as far as possible near the treatment plant so that cost of conveying
would be less.
 Water quality available in intake site should be high which will reduce treatment cost. There should
not any disposal point of wastewater in upstream of intake.
 Intake site should not locate near navigation channel due to chances of pollution of water.
 Intake site should be located so as to ensure supply in worst condition. Intake to fetch water from deeper
portion of the river and penstock may be kept two or more to take water in dry season.
 Intake site · should be located such that sufficient future extension and additions.
 The intake site should be easily accessible even during flood.
 Intake site should not locate in meandering. It should locate on the concave or outer bank so that water
available in all times.
 Intake site should be located in geologically stable and free from possibilities of erosion, silting, scouring
and heavy current.
 The intake site should be well connected by good approach road.
 In the selection of intake site the natural cause such as seasonal variations, winds, currents, climate etc.
should be studied to ensure sustainability of intake works.

General preventive measures that should be considered during design of intake structures
Proper design of intake is required for efficient and effective work. Following are the factors which
are to be considered in the design of intakes;
 Factor of safety: The intake structure should be designed with sufficient factor of safety so that it
can effectively resists the external forces due to heavy waves and currents, ice pressures, impact of
floating objects etc.
 Foundation: The design depth of foundation of intake should be sufficient so that intake could be
prevented from possible damage by the current of water.
 Protection of sides: During flood boulders may enter to intake and may be damaged so its sides
should be protected by a cluster of piles.
d) Screens and strainers: To avoid the entry of floating matters and fish in intake channel screens and
strainers are provided. If screenings allow in conduit that may clog or damage the pumps, valves
etc., and interfere during treatment works.
e) Self weight: The intake should be of adequate self-weight so that the chances of its floating or
washing by the up thrust of water may be minimized. It is essential to construct the intake structures
with masonry work and broken stones should be filled in the bottom to grant additional safety.

f) Size and numbers of inlets: Water pool level may vary season to season so adequate size and
numbers of inlets should be provided to drawing water in dry season and during flood.
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Classification of intakes
For the various surface source of water, different types of intakes are used. The various types of
intakes which are commonly used are classified as below in figure 5-1.

 Submerged intake: Intake constructed entirely under the pool is submerged intake.
 Exposed intake: When an intake is constructed with showing housing or intake tower above pool
is exposed intake.
 Wet Intake: In wet intake water is allows in intake tower or control room at get (valve) closed
condition, entry port is inside housing.
 Dry Intake: In dry intake if gets (valves) are closed there is no water inside intake tower or entry
port is directly passed into the convey pipes but operation valves are used.

5.2 Characteristics of river, reservoir and spring intakes

a) River intake
An intake tower constructed at the bank of the river to acquire water is river intake. It consists of
masonry or RCC, intake tower (housing) which is provided with several inlets (3 common) called
penstock as shown in figure 5-2.
These penstocks are positioned at different levels to permit the river water for minimum flow,
average flow and maximum flow, sometimes only two penstocks are provided. In entry port screen
is provided to prevent the entry of debris. To control or regulate the flow valves are provided in the
penstock which can be operated from control room. In control room pump is installed at the top. If
the intake tower is filled with water during get or valve closed condition it is wet intake. In dry
intake. there is no water in intake tower during get or valve closed condition.
Figure 5-2 is a typical wet river intake so that the water is always filled in the sump well of the
intake tower as wet for all the time. Wet intake can be modified to dry by connecting penstocks to
the suction pipe of the pump directly and hence water will not allowed to sump well.
In case of unstable river bed, the intake tower may be founded slightly offset from the river
bed as shown in figure 5-3. In this type of river intake, a pipe from submerged intake deliver
water to jack well then water is lifted and delivered to treatment plant through transmission
mains.

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b) Reservoir intakes
Water available in the river may not sufficient to meet demand in dry season in such case a dam
or weir across the river is constructed to meet dry demand called impended reservoir. When
intake tower is constructed in such case is called reservoir intake. There are two types of reservoir
intake (Earthen and gravity dams) commonly used. Earthen dam consists of an intake tower
constructed on the upstream toe at dam from where intake can draw sufficient quantity of water
even in the worst condition shown in figure 5-4. Penstocks are installed in different levels
through which water is withdrawn. There is provision of hemispherical screen in the entry of
these penstocks to prevent the entry of floating matters. In the penstock valves are provided to
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control and regulate the flow of water. This intake is a dry intake because there is no water inside
intake tower. For inspection and cleaning inside housing ladder or foot bridge is provided from
control room.

In gravity dam, it has two alternatives forms of intake works as having single port and
multiple ports. In Figure 5-5 an intake with 1 entry of water is through a single port which has a
trash rack structure to check the entry of debris and other floating matters. These are made in the
form of semi polygonal grid of iron or steel bars. In order to control flow generally slide gate or
sometimes valves are used which may be housed in the body of the dam itself.

In figure 5-6 an intake well is provided in the main body of the dam. Water enters the well
through inlet ports located at different levels and provided with screened opening.

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c) Spring intakes
A spring is a place on the earth's surface where, groundwater emerges naturally. An intake constructed
at the spring source to draw off water is called spring intake. Springs are generally found on hill slopes
due to geological formation as impervious layer outcrops. Generally spring water does not contain
suspended impurities and harmful bacteria. It may be used for small rural water supply scheme in Nepal.
Springs are susceptible to contamination by surface water, especially during rainstorms. Hence,
U-shaped surface drainage diversion ditch or an earth berm at least 15 meter uphill from the spring to
divert any surface runoff away from the spring has to be constructed. An area has to be fence at least 30
meter in all directions around the spring box to prevent contamination by livestock and people who are
unaware of the spring's location. To maintain discharge plantation may be done in the periphery of
spring source. Plan and section of a spring has shown in figure 5-6.
General requirements for selecting the location of the spring intake in order to get good quality
of water.
• It should be as close to source as possible.
• It should be above populated or farming (agricultural) areas.
• It should be above foot path, cattle watering and washing places.
• It should be easy to drain off surface runoff during rain.
• It should not be easy accessible to people and livestock.
• It should not allow water logging near the intake.

Factors that should be take in account or considered while constructing the spring intake.
 To prevent from the creation of backup pressure, the collection chamber needs to be constructed
away from the source by providing head· of about 4 to 5 meter of free flow to occur from the
intake
 Stone soiling below the floor should be avoided to prevent leakage.
 Heavy intake structure should be avoided to prevent from settlement.
 Adequate space in valve box should be provided so that repair and maintenance work could be
performed easily.
 Union should be provided to avoid complex problem during replacement of gate valve at the
time of repair.
 Over excavation of impervious layer at the base of the outlet of spring may lose flow so to avoid
such problem especial care required at the time of excavation.
 Inlet pipe should be covered with stone soiling and upstream of intake with impervious material
to prevent entry of suspended particles.
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 It is essential to restrict access of animals in habitation of intake at least 30 m to avoid
contamination.
 Surface runoff which occurs after rain should be easily drained off so that provision of drain in
periphery of habitation of intake should be facilitated to prevent from pollution.
 Spring of low yield less than 0.05 Ips should not be tapped for gravity flow schemes.

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Chapter seven
Reservoirs and distribution systems
To store water, a device or tank is used which is called reservoir. The storage may be public storage
(clear water reservoirs, service reservoirs etc.) and private storage (Roof tank, underground tanks in the
homes, industries etc.). The reservoirs are necessary for the following purposes:
a. To provide a reserve against failure of main or in intermittent systems of supply.
b. To meet peak demand by reserving water in other timings. (To balance the fluctuations in the
demand)
c. To reduce the pressures on the various appliances and instillations.
d. To economize the size of main pipe. (Reduces pressure then size of pipe)
e. To maintain uniform pressure in the distribution system
f. To meet the emergency demands such as fire fighting.
g. To use lighter pipes in the distribution system
The supply of water to the consumers is accomplished through a well-planned pipe networks
including; reservoirs for storing treated water, stabilizing pressures, fire hydrants, pumps, valves, service
connections, water meter etc. called distribution system.
Requirements of a good distribution system
A good distribution system should have the following requirements;
a. It should be capable to deliver treated water to consumers in adequate quantity at required pressure.
b. Water quality, should not be degraded at time of supply in distribution lines i.e. should maintain the
degree of purity.
c. It should be efficient and easy to operate and maintain.
d. It should be watertight with having minimum loss of water.
e. It should be safe against bursting of pipe due to possible excess pressure.
f. It should be capable to meet for emergencies like firefighting.

7.1 Different types of reservoir :clear water reservoir, service reservoir, balancing reservoir and
determination of capacity of reservoir
Reservoir can be classified in the following ways:
A. According to use
a. Clear water reservoir:
It is used to store the filtered water until it is pumped or conveyed into the service
reservoirs for distribution. The minimum capacity must be 14-16 hours average daily flow and
it should be divided into two or more compartments to enable repairs or clearing. The reservoirs
are generally built under ground or half below ground level and half above the ground level
depending on site conditions and constructed with masonry and RCC. Hence construction is
similar to masonry or RCC reservoir.

b. Service reservoir or distribution reservoir:·

It is used to store the filtered water from clear water reservoir and constructed before
distribution system. It is constructed with masonry and RCC. Elevated types are also popular.
These service reservoirs should be designed for balancing storage, breakdown storage and fire
storage, which will be described later.

7.2 Systems of water supply: continuous and intermittent

Treated water may be supplied to the public by the following two systems;

a. Continuous system of supply

The system in which water is supplied to the public/consumers for all 24 hours of day from the
system of supply is called continuous system of supply. This system is the most ideal system of supply

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of water which should be adopted as far as possible. This system has following advantages and
disadvantages;
~

Advantages
 Water is available throughout the day hence it is not require to private storage tank
 Water is available at the time fire fighting.
 There is no chance of sediment stagnant in the pipe due to continuous supply of water hence fresh
water is always available.
Disadvantages:
 Considerable wastage of water may occur if there is leakage.
 If the public do not realize the significance of treated water wastage and losses problem may arises,
such problem may be avoided by metering system with reasonable tariff system.
 At the period of repair and maintenance supply may be interrupted.

b. Intermittent system of supply

The system of supply in which water is supplied to the consumers for the period of fixed hours
of the day only is called Intermitted system of supply. The supply hour is fixed normally morning and
evening but time may be changed to suit the seasons of the year.
Advantages
 Useful when either sufficient pressure or quantity of water is not available at the source to meet the
demand.
 At various distribution zones of the city, water can be supplied by tum.
 Repairing work can be done in non-supply hours.
 Leakage on the system causes less waster of water because of small duration of flow.

Disadvantage
 It requires private storage tank in individual houses. If sufficient water could not store there may be
insanitary condition at the non supply periods.
 Inconvenience to consumers because people have to remain alert to collect water at supply period.
 If fire breaks out during non-supply hours, there may be great inconvenience that water could not be
available for fire fighting.
 During non-supply hour water taps may be left open unknowingly or due to negligence, which may
lead wastage at the supply period.
 This system requires large number of valves for its functioning and greater size of pipe required to
meet full day supply in short period.
 Due to negative pressure in supply line at the period of no supply may induce suction through leaking
joints causes pollution of water.
 Extra staff will be required to operate and maintain because system require number of valves for its
works to distribute water in rotation in different zones.

7.3 Layout of distribution system

After conveying water through transmission main from source to treatment plant the treated
water is stored at the reservoir to meet the hourly and daily demand. This stored water is then
distributed through a system consisting of network of pipeline with appurtenances which is called
the distribution system. Water through distribution system is taken to the individual house,
industries, commercial places, institutions and public places. Depending upon layout, the
distribution system can be classified as follows:
a. Dead end or tree or branched system
In this system, one main pipe lines laid through the center of the area to be served and from
both sides of the main pipe line sub main take off. The sub-main divide into several branches
from which service connections are given to the public. The network of pipe lines cover the
entire area as branch of tree and is no any cross connections between sub-mains and branches
and hence there may be number of dead ends in this system. This system is suitable for the
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cities or town which is growing haphazard manner without planning like our city Kathmandu.
A typical layout of tree system has shown in figure 7-7.

Advantages
 Discharge and pressure at any point can be calculated accurately hence design may be simple and
easy.
 Pipe diameters are to be design for population likely to be served which become cheep and
economical.
 Pipe lying is simple and less cut off valves required.
Disadvantages
 There is great inconvenience to consumers beyond the repair or damage due to large portion of
distribution area may be affected.
 Due to number of dead ends accumulation of sediment stagnation may lead water quality
degradation. In order to remove deposited sediment provision of scour valve may essential which
measure costly and large quantity of water required to thrown to waste.
 This system is less effective to maintain or distribute pressure in remote parts.
 Water availability for firefighting may be low because there is no chance of increase of supply by
diverting from any other side.

b. Grid-iron system Recticulation or Interlaced system

In this system, main pipeline runs through the center of the area to be served and from
both sides of the main pipe line sub-mains take off in perpendicular direction as shown in figure
7-8. Layout of mains, sub-mains, and branches are interconnected with each other. This system is
suitable for planed rectangular cities or grid iron pattern.

Advantages
 There is no sediment stagnation problem due to free circulation of water and no chances of pollution
due to sediment deposition.
 In this system, minimum head loss occurs due to interconnections of mains, sub-main, and branches.
 In case of damage or repair in any section, small area may be affected.
 For the fire fighting water could be available by diverting the supplies from other sections.
Disadvantages
 This system requires a large number of cutoff valves and longer lengths of pipe.
 Discharge and pressure calculation at any point may be tedious and time consuming and become
complex design.
 Overall cost is high

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c. Circular or ring system

In this system, entire distribution is divided into small circular or rectangular blocks and
main pipelines are laid on periphery of those blocks. Those peripheries of the mains are then linked
in interior of the area as shown in fig 7-9.In this system water can be supplied to any point from at
least two directions. This system is suitable for well planed city having planed road networks. This
system possesses the same merits and demerits as grid iron system. However pipe length, is much
longer and water availability for firefighting is large in quantity.

d. Radial system
In this system the entire area to be served is divided into a number of small rectangular
zones and in the center of each zone a distribution reservoir is provided and from which water flow
radially towards the outer periphery as in figure 7-10. Water from the main line is lifted into the
distribution reservoir. This system ensures high pressure in distribution and it gives quick and
efficient water distribution. This system is preferable for the cities having roads laid out radially.
This system possesses the same merits and demerits as grid iron system. However it requires more
reservoirs and water availability for firefighting is large in quantity.

7.4 Method of water supply: Gravity and Lift

7.5 Design of water distribution system

Distribution system design involves hydraulic and structural design of pipe. Basically in
hydraulic design size of pipe and required residual pressure in pipelines is calculated. Structural design
include determination of thickness of pipe, international pressure, external pressure, thermal stress,
thrust blocks, flexural strength etc.

7.5.1 Pipe hydraulics

Calculation of size of pipe and velocity in pipelines continuity and Bernoulli's equation are used.
A. Continuity equation
This is the equation of mathematical expression for the principle of conservation of mass flow i.e.
“Mass can neither be created nor can be destroyed until and unless nuclear reaction takes place.”

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Q=AV =constant
Q1 = A1 V1 Q2 = A2 V2
Q = Q1 + Q2 =A1 V1 + A2 V2
Where , Q and A represents Discharge and cross sectional area.
At a constant discharge; increase in size velocity will be decreased and decrease in pipe size
velocity and head loss will be increased. In pipe design velocity should be maintained such that it should
be neither silting nor scouring.

B. Bernoulli' s concept
Bernoulli's concept is the mathematical expression for the principle of conservation of energy. It
states for an ideal, incompressible, steady, irrotational flow; total energy per unit weight at any point of
flow is constant, if no energy added and taken out from the mass. Using Bernoulli's equation in pipe
design, the total energy at exist section is found by subtracting head loss from the total energy at inlet
section. Mathematically,
𝑃1 𝑣2 𝑃2 𝑣2
𝑧1 + + 2𝑔1 = 𝑧2 + + 2𝑔2 + 𝐻𝐿
𝛾 𝛾
Where,
Z= potential head
𝑃
= pressuere head
𝛾
𝑣2
= velocity head
2𝑔
𝑃
Z+𝛾 =piezometric head
P= pressure, γ= unit of water
V= velocity of water
HL= total head loss

C. Head losses in pipe

When water flows through pipes it losses energy due to fittings, change of section, wall friction,
resistance or friction in the flow result the loss of head. The following are the head loss which occurs in
flow of liquid.
a) Major loss
The major head loss is due to frictional resistance of the pipe and
can be calculated by using equations; Darcy Weisbach or Hazen
William's or Manning's equation.
i) Hazen William's equation: This is common equation in pipe design.
Velocity (V) = 0.849 CR063 s0.54
Where,. C is roughness coefficient
(Value of C; New CI=130, GI=70, HDPE= 140, Old CI= 100)
Head loss (hf) = SL
10.68𝐿𝑄 1.852
ℎ𝑓 = 𝑑4.87 𝐶 1.852

ii. Darcy Weisbach equation

This equation is used to determine the major head loss in the pipes due to friction.
𝑓𝑙𝑉 2 4𝑄
ℎ𝑓 = 𝑉 = 𝜋𝑑2
2𝑔𝑑
𝑓𝑙𝑄 2
ℎ𝑓 = 12.1𝑑5
Where, value frictional factor (f) = 0.02 to 0.075
Hf= Head loss in m, L =Length of pipe in p in m ,d =Diameter of pipe in m
V=Mean velocity of flow in pipe in m/s , g =9.81 rnls

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f =Friction factor (varies from 0.02 for new smooth pipes to 0.075 for older)

iii. Manning's equation

This equation is common for open channels flow whereas it can be used in pipe flow.
𝟐 𝟏
𝟏
𝑽 = 𝒏 𝑹𝟑 𝑺𝟐
𝟏𝟎.𝟐𝟗𝟒𝒏𝟐 𝑳𝑸𝟐
𝒉𝒇 = 𝟏𝟔
𝒅𝟑

b. Minor loss
Loss of energy due to either magnitude or the change of direction in pipe is minor loss. If the length
of pipe is large the loss of energy due to friction is cooperatively high than minor losses so it is called
minor loss and can be neglected.

7.5.2 Design criteria of distribution system

There are some criterions that should be satisfied at the design of distribution system of water.
a. Discharge
Pipe design in distribution system should be for the peak or maximum discharge. Generally for
continuous system design flow is considered as of 2 to 4 times average demand.

b. Residual pressure
Pressure in distribution line is desired for flow of water to the consumers' overhead tank and
maintains distribution equally to all consumers building situated at different elevation. In rural area
of Nepal residual pressure to be maintained should be more than 0.5 kg/cm2 . The residual pressure
required for private connections is 1.5 kg/cm2
c. Size of pipe
Pipe size should be adopted as commercially available size. The minimum size considered in
pipe design is 20 mm. Commercially available size in market are; 15, 20, 25, 32, 40, 50, 65, 80,100,
125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800,
2000, 2200, 2400, 2600, 2800, 3000 mm. It is recommended adopting on higher side of calculated
size.

d. Velocity
In pipe flow velocity should be neither silting nor scouring and should be maintained self
cleansing velocity so that sediment deposition problem in pipeline do not occur. Recommended
velocity for treated water supply is 0.3 to 3 m/sec. For unpurified water supply minimum velocity
of 0.6 m/sec may be considered.

7.5.3 Design steps involved in water supply distribution system

a. Population survey and preparation of contour maps
Population to be served needs to be surveyed and design year population is calculated with
suitable forecasting method. Topography of the area between treatment plant and distribution and
prepared with details showing roads, parks, electric lines, telephone lines, existing water supply
lines is prepared and studied.
b. Tentative layout
Tentative layout of various components like reservoirs, valves, hydrants, mains, sub-mains,
position or location is to be marked.

c. Calculation of discharge

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Based on the density of population, distribution zones and fire demand discharge is computed.
Average quantity of discharge is calculated from population and per capita demand and in
distribution line is design for peak discharge and generally it is considered as 2 to 4 times of
average discharge.

d. Computation of pipe diameters

From the contour map reduced level of difference point can be known. Adding the residual
head in elevation difference; allowable head loss in pipe can be known. Once maximum allowable
head loss obtained, using head loss equation diameter can be obtained to deliver required
discharge.

e. Computation of residual pressure and velocity

Computation of residual pressure head at any point of distribution lines can be known by
computing pressure available in the upstream points, reduced level of that point, and actual head
loss. In the context of Nepal minimum residual pressure head is 0.5 kg/cm2. For calculation of
head loss; Manning's equation is common in open channel where as Hazen William's in pipe flow
. Once diameter of pipe adopted velocity is, computed for design discharge.

7.5.4 Design of pipe networks

There are two main methods of laying of pipe networks. These are branched and looped system.
Branched system
This system is the tree or dead end system. To design the system following steps should be
followed.
a. Calculate population to be served by each section of design year.
b. Calculate design discharge for each section with the help of per capita demand, population and peak
factor.
c. Assume size of pipe for each section.
d. Calculate head loss for each section using head loss equation.
e. Check residual pressure and velocity within permissible value. Adopt the size if pressure and
velocity within allowable limits otherwise repeat the process after changing size of pipe.

looped system
Looped system consists of pipe loops; loop pipe design is complex system, It may consist of
pipe in series or in parallel. Pipe in loop may be analyzed and designed by various methods. Following
methods mostly used to analysis of a loop system.
a. Equivalent pipe method:
This method is based on the principle that;
loops are replaced by single equivalent pipe.
Equivalent pipe that can deliver equal discharge
losing equal head by given pipe system that has to
replace. Equivalent pipe method is based on
following assumptions.
 Head loss through pipes in series are
additive
 Head loss through parallel pipes are equal ·
Consider a loop of pipe network as shown in
figure below. In portion ABC pipe AB and BC and portion ADC pipe AD and DC are in series so
head loss in pipes are additive whereas pipe ABC and ADC are in parallel so head loss occurred is
equal.

Pipe in series

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Let us consider ABC portion with AB and BC pipes in series in figure 7-11 and the equivalent
pipe of length L, and diameter d,. So, head is additive and given by,
(hf)AB =(hf)AB + (hf)BC
Using Hazen William's equation
𝟏𝟎.𝟔𝟖𝑳𝒆 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟏 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟐 𝑸𝟏.𝟖𝟓𝟐
𝟏
= +
𝒅𝟒.𝟖𝟕
𝒆 𝑪𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟏 𝑪
𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟐 𝑪
𝟏.𝟖𝟐
𝑳𝒆 𝑳𝟏 𝑳𝟐
𝒐𝒓, = 𝒅𝟒.𝟖𝟕 +
𝒅𝟒.𝟖𝟕
𝒆 𝟏 𝒅𝟒.𝟖𝟕
𝟐
𝑳𝟏 𝑳
𝒐𝒓, 𝑳𝒆 = 𝒅𝟒.𝟖𝟕
𝒆 [𝒅𝟒.𝟖𝟕 𝟐
+ 𝒅𝟒.𝟖𝟕 ]
𝟏 𝟐
Generalizing pipes in series
𝑳 𝑳
𝑳𝒆 = 𝒅𝟒.𝟖𝟕
𝒆
𝟏
[𝒅𝟒.𝟖𝟕 𝟐
+ 𝒅𝟒.𝟖𝟕 +⋯]
𝟏 𝟐

Pipes in parallel
Consider ABC and ADC pipes in parallel in figure 7-11 and let the equivalent pipe of length Le
and diameter de. Then head loss occurred in parallel pipes is equal and given by;
(hf)AC =(hf)AB + (hf)BC = (hf)AD + (hr)DC
Using Hazen William's equation
𝟏𝟎.𝟔𝟖𝑳𝟏 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟐 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟑 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟒 𝑸𝟏.𝟖𝟓𝟐
𝟏
+ = +
𝒅𝟒.𝟖𝟕
𝟏 𝑪
𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟐 𝑪
𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟑 𝑪
𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟒 𝑪
𝟏.𝟖𝟐
𝟏
𝑳𝟑 𝑳𝟒 𝟏.𝟖𝟓𝟐
𝟒.𝟖𝟕+ 𝟒.𝟖𝟕
𝑸 𝒅 𝒅𝟐
[ 𝑸𝟏 ] = ( 𝟏𝑳𝟏 𝑳𝟐 ) =𝑲
𝟒.𝟖𝟕+ 𝟒.𝟖𝟕
𝟐
𝒅𝟏 𝒅𝟐
Therefore; Q1 =Q2K
Again, Q= Q1 + Q2 = Q2 (K+1)
If the length and diameter of equivalent pipe causing equal head loss between A and C are Le and d,.
(hf) AC =(hf) AD + (hf) DC
Using Hazen William's equation
𝟏𝟎.𝟔𝟖𝑳𝒆 𝑸𝟏.𝟖𝟓𝟐
𝟏 𝟏𝟎.𝟔𝟖𝑳𝟑 𝑸𝟏.𝟖𝟓𝟐
𝟐 𝟏𝟎.𝟔𝟖𝑳𝟒 𝑸𝟏.𝟖𝟓𝟐
𝟐
= +
𝒅𝟒.𝟖𝟕
𝒆 𝑪𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟑 𝑪
𝟏.𝟖𝟐 𝒅𝟒.𝟖𝟕
𝟒 𝑪
𝟏.𝟖𝟐

𝑳𝒆 𝑳𝟑 𝑳𝟒
or, (𝑲 + 𝟏)𝟏.𝟖𝟓𝟐 = [ + ]
𝒅𝟒.𝟖𝟕
𝒆 𝒅𝟒.𝟖𝟕
𝟏 𝒅𝟒.𝟖𝟕
𝟐
𝒅𝟒.𝟖𝟕
𝒆 𝑳
𝟑 𝟒 𝑳
∴ 𝑳𝒆 = 𝟏.𝟖𝟓𝟐 [𝒅𝟒.𝟖𝟕 + 𝟒.𝟖𝟕 ]
𝑸 𝟏 𝒅 𝟐
( 𝟏 +𝟏)
𝑸𝟐

7.5.5 Hardy Cross Method

It is a method of successive approximations involves a controlled trial and error process. This method
is based on following three laws.
a. In each pipe of the network there is relationship between the head loss in the pipe and discharge through
it i.e. hf = r Qn where r and n are constants.
b. At each junction the algebraic sum of the quantities of water entering and leaving the junction is zero
i.e. ΣQ= 0.
c. In each loop head loss due to flow in clockwise and anticlockwise must be equal to zero i.e. Σhf = 0.

The analysis of pipe network by Hardy Cross method can be done by any one of the following method.
a)Balancing head by correcting assumed flows
This is the common Hardy Cross method used when the flow of water entering and leaving in
the network is known. In this method loss of head in the loop is balanced by the correction of assumed
flows.

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Let, Q is correct flow and Q0 is assumed flow in the pipe. Then,
Q=Qo+ΔQ
Where, ΔQ is flow correction
If hf is head loss in pipe under reference;
Hf= r Qn where r and n is constant
Now, hf= r (Q0 + ΔQ)"
Hf =𝑟(𝑄𝑜𝑛 + 𝑛𝑄0𝑛−𝑖 ∆𝑄 + ⋯ + ∆𝑄 𝑛 )
If ΔQ is small compared to Q0 all terms of the series after the second one (higher power) may be
neglected.

Value of n =2 for Manning's and Darcy Weisbach equation. For Hazen William's equation n= 1.852

Steps involved in this method

 In a junction, assume suitable Qo in each pipe so that ΣQ = 0 (inflow positive and outflow negative)
 Compute hr in each pipe considering hf = r Qn (assume hr positive for clockwise Q0 and negative
for anticlockwise Qo in the loop)
 If Σhf = 0, assumed flow (Q0 )will be ok. If not, calculate flow correction by

 For common pipes in the two loops correction from both loops is required.
 Repeat trials with corrected flow till AQ become negligible.

b) Balancing flow by correcting assumed heads

This is the modification of original Hardy Cross method and useful in case of unknown discharge and
having several inlets in the pipe network. In this method, flows at each junction are corrected for
assumed heads at the junction and the corresponding head loss in pipes.

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Chapter eight
Conveyance of water
After collection of water from intake it is conveyed to treatment plan( or reservoir or distribution
through conduits. Conveyance from intake to treatment plant and treatment plant to reservoirs is called
transmission and reservoir to consumers tap is called distribution. If the source is at the higher elevation,.
it can be conveyed through conduit under gravitational force otherwise pumping is required.
Conduit: It is the device used to carry water. In the ancient times water is conveyed through open
channels or wooden log channels. Slowly the use of masonry chamber of rectangular and circular are
introduced and then these open channel was closed from top. Normally conduits can be classified into:
(a) Gravity conduit:
These are the conduits in which water flows under the action of gravity and there is a free water surface
exposed to the atmosphere (open channel flow).Eg· Canals, aqueducts, tunnels etc.

(b) Pressure conduit:

These are the conduits where water can flow under pressure.· Egg: pipes, pressure tunnels, pressure
aqueducts etc. Pressure conduits can follow the· natural ground surface and can be taken up and down
hills within the HGL hence lesser length of conduit is achieved. A pressure conduits when taken along
a hill may rise above the HGL it is called a siphon.

8.1 Different types of pipe: CI, GI, WI, steel, concrete, Ac and PVC
Pipes are circular conduits which can carry liquid in pressure are of various sizes and different
materials. in case of drinking water conveyance and distribution circular pipes are mostly used. Pipes
are of different materials as GI, DI, CI, WI, steel, cement concrete, HDPE, PPR, PVC etc. Selection
of pipe materials depends upon fund availability, type of water to be conveyed and its life span and
durability, corrosive properties, resistant to temperature stresses, ability to resist pressure, repair and
maintenance cost etc.

Types of pipe materials

The pipes are usually classified according to the materials which are as follows;
D. Cast iron pipe (CI)
These pipes are widely used for the conveyance of water in water supply scheme. These pipes
are highly corrosion resistant and possess other desirable properties like durability, easy to make joint,
long life, strong and can resist maximum pressure likely to develop. Cast iron pipe are expensive and
heavy hence difficult to transport.
CI pipes are available in 2.5 to 5.5 m length with various diameters. According to thickness CI pipes are
classified as LA, A and B class and can resist pressure of 10, 12.5 and 16 kg/cm2 respectively.
Advantages of Cl pipe
 Cost of these pipes is moderate.
 The pipes are easy to join.
 The pipes are highly resistant to corrosion.
 The pipes are strong and durable
 Service connections can be easily made
 Usual life is about 100 years

Disadvantage of CI pipes
 CI pipes are heavier so that difficult in handling and transport.
 The carrying capacity of these pipes decreases with the increase in life of pipes due to tuberculation.
 These pipes generate metallic taste in the water due to the iron leaching into the water from the
rusting of the pipe.
 These pipes are brittle.
 Since CI pipes are heavier use of larger size become uneconomical.

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E. Galvanized iron pipe (GI pipe)
These are the mild steel or wrought iron pipes, provided with a protective coating of zinc on
the both inner and outer surface. These pipes are commonly used in house plumbing or after service
connection. For water pipe fittings 12 mm to 25 mm diameter pipes are used and available in a
length of 7 m. These pipes are cheap, light, easy to join, easy to transport and handling. The life
span of these pipes is around 20 years. GI pipes may get corrode by acidic or alkaline or otherwise
activated waters also liable to insulation. In water if chlorine is added as disinfectant, an increase
in corrosion of iron materials can be expected.
Advantages of GI pipes :
 These pipes are cheap.
 Light in weight and easy to handle.
 The pipes are easy to join.
 These pipes can be easily cut and threaded.

Disadvantages of GI pipes
 The pipes are affected by acidic or alkaline waters.
 The pipes are less durable.
 Hydraulic efficiency decrease with time as decreases smoothness.

F. Wrought iron (WI) Pipes

WI pipes are manufactured by rolling the flat plates of metal to proper diameter and welding to
the edges. It is made of WI and can be joined by coupling or screw or socket joint. These pipes are
Suitable for inside plumbing in buildings but not used nowadays due to high cost.
Advantages of WI pipes
 These are Light in weight
 These are easy in transport
 These are easy in handling, cutting, threading, working,joining
 These pipes gives neat appearance

Disadvantages of WI pipes
 The pipes are Costly
 The pipes are corrosive
 The pipes are less durable than CI pipes.

G. Steel pipe
These are fabricated by rolling the mild steel plates to proper diameter and can jointed by riveting or
welding. These pipes are strong, cheaper, light in weight, can resist high pressure up to 400 m. The
welded steel pipes are made up to 2.4 m in diameter and up to 12 m length. Theses pipe are costlier,
liable to corrosion, and can't resist pressure due to external load during vacuum inside.
Advantages of Steel pipes
 Numbers of joint are less because these are available in long lengths.
 The pipes are cheap in first cost.
 The pipes are durable and strong enough to resist high internal water pressure.
 The pipes ·are flexible to some extent and they can therefore laid on curves.
 Transportation is easy because of light weight.

Disadvantages of Steel pipes

 Maintenance cost is high.
 The pipes are likely to be rusted by acidic or alkaline water.
 The pipes require more time for repairs during breakdown and hence not suitable for distribution
pipes.

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 The pipes may deform in shape under combined action of external forces.

H. Polyvinyl chloride (PVC) pipe

PVC pipes are made of combination of plastic and vinyl. These plastic pipes are highly rigid,
easy to join, strong in resisting pressure, light in weight hence transportable, can resist acids, alkalis,
salts and organic chemicals, cheaper so commonly used in Nepal. This pipe requires support closer due
to flexibility so that can break or crack if miss-handled. PVC pipes can resists temperature up to 60 °C.
A minimal skills and tools are required to install PVC pipes. As they do not rust, rot, or wear over a
time, these pipes are commonly used in water systems.
Advantages of PVC pipes
 Pipes are cheap.
 The pipes are durable.
 The pipes are flexible.
 The pipes are free from corrosion.
 The pipes are good electric insulators.
 The pipes are light in weight and it can easy to mould any shape.

Disadvantages of PVC pipes

 The co-efficient of expansion for plastic is high.
 It is difficult to obtain the plastic pipes of uniform composition.
 The pipes are less resistance to heat.
 Some types of plastic impart taste to the water.

I. Polypropylene random copolymer (PPR) pipe

Polypropylene random copolymers are thermoplastic resins produced through the polymerization of
propylene, with ethylene links introduced in the polymer chain. Homopolymer, random copolymer, and
block copolymer are the types of polypropylene. These pipes are highly resistant to temperature and
impact load. These pipes can resist temperature up to 70 °C so it can be used for hot water supply.
Nowadays PPR pipes and fittings are popular in plumbing and water supply plants due to easy in joint,
perfect seal tight system, no calcification problem, durable and long life expectancy, non-deforming, no
reaction with salts and acids, eco friendly, recyclable, good chemical resistance etc.
Advantages of PPR pipes
 These pipes perform good hydraulic efficiency.
 Light in weight and easy to handle.
 The pipes possess high resistivity against heat.
 These pipes are eco friendly and durable.
 It performs good resistivity to chemicals.
 Calcification problem does not arise in these pipes.
 Life expectancy of these pipes is of more than 50 years.
Disadvantages of PPR pipes
 Joining and repairing of PPR pipes is possible by use of a fusion -welding tool.
 As PPR pipes are plastic product exposed to direct sunlight may drying out the oil content present
in all plastics.

J. Ductile iron (DI)pipe

These pipes are made of ductile iron commonly used for potable water transmission and
distribution. Typically, the pipe is manufactured using centrifugal casting in metal or resin lined molds.
Protective internal linings and external coatings are done to ductile iron pipes to overcome corrosion
problems. Hence these pipes are highly corrosion resistant and long life (100 yrs.).
Advantages of DI pipes
 Comparatively DI pipes possess greater ductility and impact resistance then CI pipes.
 Lighter than CI pipes so that easy to handle and transport.

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 The pipes are easy to join and simple also can accommodate some angular deflection.
 These pipes are of more strength than CI pipes.

Disadvantages of DI pipes
 The pipes require internal and external lining or protection.
 Corrosion may take place as equal in CI pipes.
 The polyethylene wrappings may cause damaged.

K. Concrete pipe
Cement concrete p1pe pipes may be either plain cement or reinforced cement concrete. PCC pipes
can be used up to 15 m head where as RCC pipes can be used up to head of 60 m and for higher head
pre-stressed concrete can be used. These pipes are also called on situ pipe so that they may be casted in
site also. Pipes of reinforced pipe are also known as Hume pipes. These pipes are non-corrosive and
longer life. The maintenance cost of cement concrete pipe is less and joints are very simple. However,
concrete pipes are inconvenient as they are heavy, less resistance to withstand impact and shock.
Advantages of concrete pipes
 There are pipes are most durable with usual life of about 75 years.
 The pipes can cast at site work and thus there is reduction in transport charges.
 Maintenance cost is less.
 Inside surface of pipe can made smooth.
 No danger of rusting.

Disadvantages of concrete pipes

 Transportation is difficult.
 Repair work is difficult.
 Initial cost is high.
 These pipes are affected by acids, alkalis and salty waters.

L. Asbestos cement (A C) pipes

It is made of mixture of cement and asbestos fibers, manufactured in 5 to 130 cm diameter, resists
internal pressure of 3.5kg/cm2 pressure.
Advantages of AC pipes
 It is not affected by salt water and corrosive material.
 It remains smooth.
 It is light so easy in handling.

Disadvantages of AC pipes
 It is affected by alkali and acid
 It is brittle so costlier in transport.
Suitability: Suitable for small size distribution pipes.

8.2 Laying of pipes

The various operations involved in laying of pipes are as indicated below:
1. Preparation of detailed maps showing alignment of pipelines:
Survey is conducted to prepare detailed map showing alignment of pipelines from source to
treatment plant and distribution network and also map should show the position of roads, sewer
lines, existing water pipes, telephone lines, electric lines etc.

2. Locating the proposed alignment of the pipe line on the ground:

The alignment of pipeline is marked by pegging in 30 m interval on straight and 7.5 to 15 m
apart in curves.

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3. Pipe laying with respect to ground level:
Pipe laying is of transmission main may be above ground level but support at a suitable interval
may be required to prevent from settlement where as distribution network are laid below the ground
surface.

4. Excavation and preparation of trench:

Excavation may be done mechanically or manually as per specification but it is commonly done
manually in Nepal. Trench should excavated by adding 30 to 45 cm in external diameter of pipe.
More than 90 cm clearance is provided above crown but 15 to 20 cm more excavation is done both
directions (Horizontal and Vertical) at the place of joint. The bottom of the trench carefully prepared
so that the pipe can be laid true to line and gradient and also there would be adequate protection
against possible settlement

5. Dewatering of trench:
If GWT coincide at the trench level dewatering may be required which could be done by pumping
or gravity method.

6. Lowering of pipes into the trench:

Pipe should be transported carefully to site and lowered by stacked on one side (one side
construction material and earth material in other side). Protective coating and pipe end should not
be damaged.

7. Joining pipe:
Proper types of joint should be selected and joined. Valves should be fitted at proper places along
the pipeline.

8. Testing of pipes:
Leakage test should be done at a suitable section of about 500 m length. Water is pumped twice
the normal Operation pressure from one end and next end is closed for 24 hrs. Allowable leakage
may be known by following formula:
ND(√𝑃)
Q=
3.3
where, Q = allowable leakage cm3 /hr.,
N =No of joints to be tested,
D = Diameter in mm
P =Average test pressure Kg/cm2
.
9. Disinfection and back filling of trench:
Disinfection is done by adding chlorine 50 ppm for 12 hrs. Backfilling is done by parent material
with suitable compaction method up to 15 cm above GL.

8.3 Pipe joints and their types

Pipe joints
For the ease in handling, transporting and placing in position of pipe, these are manufactured in suitable
length hence pipe should be jointed together after placing in the position for continuation. A joint may
require at bent to change direction of pipe or to connect pipe for continuation of pipeline which is called
pipe joint. ·Hence proper joint should be used as per condition, material of pipe; internal water pressure
and condition of support.
Types of pipe joint
Following types of joints are commonly used in water supply pipe lines:
 Socket and spigot (bell and spigot joint)

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This joint as shown in figure 8-1 is commonly used for CI pipes as well as DI pipes. In this joint
spigot of one end of the pipe is slipped
in socket or bell end of other pipe and
jute or hemp yarn is wrapped around
spigot tightly up to 50 mm depth and a
gasket or joint runner is clamped in
place of round joint to fit tightly. By
the help of chalking tool molten lead
poured into the V shape opening left
on the top by clamped joint runner.
Space between hemp yam and
clamped runner is filled with molten
lead. Now runner is removed after
hardening of lead then tightened by
chalking tool and hammer. Lead about
3.5 to 4 kg may required for up to the
diameter 150 mm and for diameter 120 cm pipe 40 to 45 kg per joint. It takes high cost but makes
joint perfect.

 Flanged joint
This joint is commonly used for CI
pipes, steel pipes and GI pipes. This joint as
shown in figure 8-2 may be used for
temporary works so that it can easily
assemble and dissemble. The flanges of
both pipes brought together and placing
gasket in-between it is water tightened by
screw or welding. This joint is suitable for
pumping station filter plant, laboratories
and boiler house but not used in place
having vibration and deflection.

 Expansion joint
This joint can bear temperature stress which
results expansion and contraction. Function of this
joint is to maintain water-tightness of the joint due
to stress produced by temperature variations.
Socket end is flanged with cast iron follower ring
which can be freely slide on the spigot end and a
rubber gasket is tightly pressed between angular
space of spigot and socket by means of bolt as
shown in figure 8-3. Water-tightness is maintained
by rubber gasket during slight movement of socket
end in forward and backward directions due to
temperature stress.

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 Collar joint:This joint is commonly used for cement concrete pipes; both reinforced and pre-stressed
concrete pipes with plain ends. Tow ends of pipes are brought in same level with rubber gasket in-
between, collar is placed with lap on both pipes. Cement mortar (1: 1) is filled between the space of collar
and pipe. (See figure 8-4)

 Screwed and socket

Screwed and socket joint as shown in figure 8-5 is commonly used for GI pipes and also for
small diameter steel pipes. Ends of the both pipes have screw threads on the outer surface in which
socket are screwed to make the joint

 Mechanical joint
It is used in CI, steel or WI pipes when both end are plain or spigot. Dresser coupling
mechanical joint is used in water supply over bridge to bear vibrations.

 Flexible joint
This joint is used where settlement is likely because of its flexibility. This type of joint is
shown in fig 8.7

 AC pipe joint
It is used for small diameter AC pipes. In this joint, butt ends are put against each other and
two rubber rings will be slipped over the pipes and coupling is pushed. Rubber rings make leak
proof.

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Chapter nine
Valves and Fitting
Those devices which are used in water supply systems to control the flow of water, to regulate
pressures, to release air, to prevent back flow and for other purposes are called valves.
Similarly, various devices are used in water supply systems to connect pipes as well as in the
outlet indoor or outdoor to convey and get water are called fittings.

9.1 Different types of valve: sluice valve, reflux valve, safety valve, air valve, drain valve
The various types of valves commonly used are as follows:
9.1.1 Sluice or gate or cutoff valve
These are the commonly used valve to regulate the flow of water through pipelines. These valves
as shown in figure 9-1 are extensively used in the distribution system to shut off the supplies. It consists
of a disc or circular gate parallel sided or wedge shaped in cross-section and having a nut which slot in
with the thread of an operating spindle. The disc or circular gate, by raising or lowering flow can be
regulate or control. These valves may be provided in every junction and in a suitable interval of about
150 to 300 m in straight portion. These valves are operated by rotating the spindle in clockwise to close
and anticlockwise to open.

9.1.2 Reflux (check valve)

When flow is to be maintained in one direction only in the pipe, a valve is used which is called
reflux or check or non-return valve. It consists of a disc hinged at its top edge provided at the one end
in such a way that it opens when flow is forward and closes if water tends to flow in reverse direction.
This valve is invariably placed in a pumping main. Figure 9-2 shows the check valve of horizontal type.

9.1.3 Safety or pressure relief valve

The valve which is use to release the unwanted pressure , when the pressure in the pipe line is
maximum is known as safety valve or pressure release valve. It consists of a disc controlled by spring
which can be adjusted to desired pressure. It is provided to release the excessive pressure from the
pipeline and protect the pipeline against possible danger of bursting due to excessive pressure. When
the pressure in pipelines exceeds the desired pressure, the disc is forced to be lifted up and certain
amount of water flows out from the cross pipe thereby releasing the pressure in the pipeline. This valve
is also called automatic cutoff valve as shown in figure 9-3.

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9.1.4 Air relief or air valve

In a pipeline air may enter or entrained air get trapped which may be accumulated in summit or
high points of pipeline and may be serious blockade to flow of water. It consists of a CI chamber, float,
lever and poppet valve is held in closed position. The chamber is connected to the bolted on the pipe top
opening in the crown. A float mass and a lever in it are adjusted and the chamber is filled with water
under pressure from the pipe below, the float remains raised up and opening is closed. If there is no
water but accumulated air in the chamber, the float sinks then the opening. is opened and all air is
released. (see figure 9-4)

9.1.5 Drain or scour valve

Water may carry sand and silt which .:nay be deposited in the pipe line (normally in intermittent
system). To emptying or draining the pipe for removing sand or silt deposited in the pipe and for
inspection; repair etc., an ordinary sluice valve is placed at the dead ends and at depressions (lowest
point) is called the drain or blow off valve. They are ordinary sluice valves operated by hand. They are
located at the depressions and dead ends to remove the accumulated silt and sand. After the complete
removal of silt; the valve is to be closed.

9.2 Different types of pipe fitting :stop cocks, nipples, sockets, joint coupling water taps and bends
9.2.1 Fittings for pipe
Various fittings commonly used .in pipe network are shown in figure 9-5 such as unions, caps,
plugs, flanges, nipples, crosses, tees, elbows, bend etc.

9.2.2 Stop cocks and water taps

Stop cock is a valve fitted at the end of communication pipe (communication pipe is owned
and managed by the water supply authority) just outside the property boundary to isolate the house
from the water supply at the period of maintenance of system inside the house. The stop clocks
are particularly sluice or gate valve of small size. Temporary disconnections are made at the
stopcock while permanent disconnections are made at ferrule. Figure 9-6 shows a stop Cock.

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Water taps are also known as bib cocks or faucets. These are attached at the end of water pipe
line in wash basins, kitchens, bathrooms etc. from which the consumers obtained water. Water taps
are operated by handle as shown in figure 9-7.]

9.2.3 Water meters

These are the devices which are installed
on the pipes to measure the quantity of
water flowing at a particular point along
the pipe. The readings obtained from the
meters help in working out the quantity of
water supplied and thus the consumers can
be charged accordingly. The water meters
are usually installed to supply water to
consumers metering prevents the wastage
of purified water. A rotary type water meter is shown in figure 9-8.

9.3 Public stand post and break pressure tank

9.3.1 Break pressure tank
BPT is a small tank or chamber provided in order to break the excessive hydrostatic
pressure in the pipeline. In this tank the water freely discharges and hydrostatic pressure is
reduced to zero thereby establishing a new static water level hence these tanks may also known
as pressure releasing tank. A simple BPT has shown in figure 9-9 and these are generally provided
in gravity flow water supply system to prevent the pipeline against possible danger of bursting
due to excessive pressure. This tank may be circular or rectangular in shape and made of
masonry, RCC or Ferro cement. It is closed chamber with provision of different valves as inlet,
outlet, overflow, float (to prevent from overflow) etc. Reservoir may also act as BPT. When level
difference (head) exceeds then that of capacity to withstand pressure by used pipe in gravity flow
system a BPT is provided. The strategic provision of BPT in pipelines can avoid or minimize the
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use of high pressure rating pipes and optimizes the system cost. HDPE pipes with pressure ratings
of 4 kg/cm2, 6 kg/cm2 and 10 kg/cm2 are widely used. to convey the water in gravity flow water
supply system and when pressure exceeds 10 kg/cm2 GI pipes are used.

9.3.2 Public stand post

Public stand post is last component of water supply schemes from where people collect water
to meet their household demand in rural area. Public stand post should be located at a suitable

place as convenient for washing, laundering and filling water, aesthetically pleasant, clean and
inviting and also generated wastewater should be easily drained off. Generally walking distance
for fetching water should not be more than 50 m (80 min exceptional case) in vertical and 200
m (250m in exceptional case) in horizontal. A stand post is designed to serve 8 to 10 households.
A public stand post should serve maximum of 100 users.
The minimum discharge in a stand post should not be less than of 0.1 Ips and maximum
discharge is limited to 0.25 Lps, for adequate provision it should be of 0.15 Lps. When flow in
a public stand post is 0.1 Lps, 2.5 minute is required to fill a vessel of 15 liters. A tap stand will
adequately serve a population of about 100 persons at an average per capita demand of 45
liters/day with peak factor of 3.
Construction of a tap stand includes several components: a post supporting a 15 mm mild
steel riser pipe from the pipeline up to a bibcock or faucet which should discharge at least 0.1
Ips; a stand on which to place a bucket; a apron to collect spillage; and a gutter and drainage to
a soak way in order to prevent the breeding of flies and mosquitoes and to keep the area clean.
The height of the faucet should be 1300 mm in average above the apron. Normally faucet is not
protruding more than 300 mm.

9.4 Operation and maintenance of water supply system

Maintenance may be defined as the repairing of damaged things. As per repair works
maintenance can be classified as preventive emergency and regular. These are described below

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Methods of maintenance of water supply system
1. Preventive maintenance
Especially in rainy season sediment accumulated in source, in pipelines should be removed on
time so that possible risk could be minimized. Drainage facilities, plantation, protective walls may
be done or construct to protect from further damage, such works are preventative maintenance.
2. Regular maintenance
For the protection of components of water supply cleaning and replacing of devices is regularly
done in a suitable interval of time is called regular maintenance.
3. Emergency maintenance
Natural disasters like flood, landslide may damage components of water supply like reservoir,
pipelines, valves, source etc. At that time immediate maintenance may be required for proper
functioning of water supply project called emergency maintenance.

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