PRINCIPLES OF PLANNING AND DESIGN:

APPLIED TO DESIGN OF WATER RESERVOIRS, TRUNK MAINS, AND

TOWNSHIP DISTRIBUTION

This will involve:

- Components of water supply system
- Typical town/ village water supply system
- Sources of water
- Water treatment
- Water supply mechanism
- Storage facilities
- Types of water supply
Water supply is essential to enhance the capacity of a community in development
through provision of water to residential for drinking, cooking, sanitation, and also
to enable operation of business and industry. Of no less importance is the need to
provide water to properly located fire hydrants to provide the public with effective
level of fire protection. Hence it is important to have insights on basic components
of water supply systems, installation and distribution, estimation and
measurements of components of water supply systems and drinking water quality
control.
The main purpose of a water distribution system is to deliver water to the
consumer with the appropriate quality, quantity, and pressure plus meet the
required fire flow. The water system should be reliable; should meet the required
amount of water needed to be available 24 hours a day, 365 days a year.
Distribution system is to describe collectively the facilities used to supply water
from its source to the point of usage.

Typical piped water supply system (components):

- From the source the water is retained in holding reservoirs that supply water
to the treatment plant that processes the water to remove impurities and
add chemicals to bring the water in compliance with the regulations on
clean water for drinking and commercial usage. The purified water, or
finished water (potable water), is then pumped to several storage tanks for
release into distribution system piping network on demand for consumer
use or in the case of a fire. Depending on the different elevation points
throughout the city/village, additional pumping stations are provided to
maintain adequate pressure in the water system during varying periods of
consumer use or emergency water supply demand requirements. Water
flows from the storage locations through the primary, secondary, and
distributor mains to supply service lines to individual consumers and
lateral lines to supply fire hydrants.

Source Holding Treatment Storage

reservoir
s

Distribution
Primary

Secondary

Distributor mains

Service lines
To consumers Lateral line to
fire hydrant

Fig. 1: Typical Piped water supply system

Sources of Water.
There are three main sources of water: surface water, groundwater, and rainwater.
a) Surface Water is found in lakes, rivers, and reservoirs (ponds and dams)
where surface water is available.
b) Groundwater lies under the surface of the land, where it travels through and
fills openings in the rocks. The rocks that store and transmit groundwater are called
aquifers. Groundwater must be pumped from an aquifer to the earth's surface for
use. Sources of ground water include:
- Open wells; where ground water is available at low depths (less than 15 m –
and water is available all year round.
- Hand pump; where safe ground water is available upto 60 m depth. Hand
pump is suitable for a cluster habitation.
- Bore well/ Tube well; where ground water is at greater depth and open wells
or hand pumps are not viable, bore well or tube well is installed.
c) Rain Water; Rain water can be harvested and stored directly in storage tanks.

Assessing Water Availability

Availability of water from the source can be assessed to determine its suitability as
a source of water for the given community/ municipality.
1) Estimating water availability from Ponds/lakes;
Let; a – size/capacity of pond, m3 or litres (1000 litres = 1 m3)
b – Number of filling per year,
then, Total Capacity of storage = a × b m3
Nb/: For number of fills, it can be partial or full
Partial – 0.25 – 0.75
Full – 1
2) Estimating water availability from community hand pumps;
Let; a – number of sources
b – average working hours per day
c – average discharge rate per hour (can be estimated to 12
litres/minute, or 720 litres /hour)
d – per day water availability
Then; d = a×b×c
If e is number of fuctional days in a year;
Total water availability in a year (litres) = d×e
3) Estimating water availability from community bore/tube well;
- Water availability from bore well can be determined from discharge rate of
pump placed for drafting.
 Bore Discharge rate Average Total water Average number of Water
well of water pumping hours availability, days of water availability in a
Litres/hour in a day Litres/day availability per day year, Litres/Year

1 a b c = a×b d e = c×d

Total water availability in a year = sum of this

column

Notes:
- Discharge rates can be estimated from average volume of tank filling in an
hour.
- pumping is normally done from 8 – 12 hours per day
4) Estimating water availability from external piped supply;
- various methods can be adopted, such like;
- Method 1:
Through average volumetric measurements through water meters installed.
Let; a – water availability, litres/day
b – average days of water supply in a year
Thus, Total yearly water availability = a × b
- Method 2
a – number of fillings of main storage tank at village/town in a day
b – capacity of main storage tank
Available water per day = a × b

Assessment of water demand gap;

Let; a – Yearly water demand
b – Yearly water availability
c – Yearly water gap; c = (a – b)
Water System Demands.

The demand for water supplied by a water supply system has two driving
components:
1) consumer consumption: the amount of water in litres/min or litres per day that
is used by all of the taps on the water mains to supply single-family homes,
multiple-family residences of all types, health care facilities, schools at all levels of
education, commercial enterprises, industrial complexes, and adjunct uses (street
cleaning; water fountains; watering public grass areas; shrubs, trees, and flowers;
parks and recreation including swimming pools; and the sale of water to
contractors for building roads, structures, etc.) and
2) An adequate and reliable water supply for fire protection.
Some important terms associated with water demand are:
a) Consumer consumption: Consumer consumption is assessed by
determining the amount of water that actually is used by consumers, based on three
levels of usage as follows:
i) Average daily consumption (ADC): This is the average of the total amount
of water used each day during a 1-year period (usually expressed in million
Litres per day, MLD). Each municipal water system services a defined
population as determined by census figures. For example, assume that the
municipality in question has a population of 22,570. It was determined from
water meter readings that the average daily consumption was 137 liters per
person per day or the community consumed 22,570 × 137 litres = 3,092,090
litres. This means that on an average day, the water supply works need to have
available nearly 3.1 million litres of water over a 24-hour period, or an average
delivery rate of 2,147 lpm of finished water delivered into the water supply
distribution system.
The number 137 lpm reflects the total amount of water used in a day by the
population and inclusive of usage by different classes of occupancy including
commerce and industry.
ii) Maximum Daily Consumption (MDC): This is the maximum total amount of
water used during any 24-hour period in a 3-year period. This number should
consider and exclude any unusual and excessive identified used of water that
would affect the calculation. Such abnormal uses would include a water main
break, a large-scale fire, or an abnormal industrial demand. This value
represents the single day within a year-long period on which the consumption
rate was the highest. The MDC rate for any given community is approximately
150 percent of the ADC rate. For the average community considered, this
would be 205.5 litres per day per person. The MDC rate often is reached in the
summer months or during times of peak water demand for industrial use.
iii) Instantaneous flow demand: There are generally two peak periods in the day
when consumption is greatest: between 7 a.m. to 9 a.m. and between 5 p.m. to 7
p.m.
The water supply superintendent, or a person of equal responsibility, has to predict
these rates in order to control the amount of water delivered to the water
distribution system and water pressure such that any given tap can supply water at
the desired pressure.

iv) Maximum hourly demand: This is the maximum amount of water used in any
single hour, of any day, in a 3-year period.

b) Fire flow demand: At any time, the municipal/village water supply system
should be able to deliver needed fire flows to representative fire risks throughout
the community from properly located fire hydrants.
An adequate amount of water is essential to confining, controlling, and
extinguishing hostile fires in structures. The actual amount of water needed
differs throughout a municipality/village, based on different building and occupant
conditions. Therefore, water damage for structural fire protection must be
determined at a number of different locations throughout a given municipality or
fire protection district. These locations are selected by the Insurance Services
Office to represent typical fire risks, including residential, commercial, mercantile,
institutional, and industrial properties for insurance rating purposes.

Per Capita Water Demand

The concept of per capita water use is often used for comparing water use over
time or among groups of people (cities, counties, etc.) that use public water
supplies (e.g., city water). Generally, Per capita water demand means the average
amount of water each person in a particular area uses on a daily basis throughout a
year, expressed as “litres per capita per day.” Per capita demand includes all the
water used in and area within a period of one year (water used in firefighting,
industry, commercial enterprises, residential, institutions, construction, losses
through leakages and theft, gardens, and all such uses.

Average Daily Per Capita Demand

= Quantity Required in 12 Months/ (365 x Population)

Factors affecting per capita demand:

a. Size of the city: Per capita demand for big cities is generally large as
compared to that for smaller towns as big cities have sewered houses.
b. Presence of industries.
c. Climatic conditions.
d. Habits of people and their economic status.
e. Quality of water: If water is aesthetically $ medically safe, the consumption
will increase as people will not resort to private wells, etc.
 f. Pressure in the distribution system.
g. Efficiency of water works administration: Leaks in water mains and
services; and unauthorised use of water can be kept to a minimum by
surveys.
h. Cost of water.
i. Policy of metering and charging method: Water tax is charged in two
different ways: on the basis of meter reading and on the basis of certain
fixed monthly rate.

How Are Per Capita Water Rates Used?

Water managers use per capita measurements for a number of purposes
such as:

ting conservation program effectiveness, and

.

Fluctuations in Rate of Demand

If the average demand is supplied at all the times, it will not be sufficient to meet
fluctuations.

 Seasonal variation: The demand peaks during summer. Firebreak outs are
generally more in summer, increasing demand. So, there is seasonal
variation .
 Daily variation depends on the activity. People draw out more water on
Sundays and Festival days, thus increasing demand on these days.
 Hourly variations are very important as they have a wide range. During
active household working hours i.e. from six to ten in the morning and four
to eight in the evening, the bulk of the daily requirement is taken. During
other hours the requirement is negligible. Moreover, if a fire breaks out, a
huge quantity of water is required to be supplied during short duration,
necessitating the need for a maximum rate of hourly supply.
So, an adequate quantity of water must be available to meet the peak demand. To
meet all the fluctuations, the supply pipes, service reservoirs and distribution
pipes must be properly proportioned. The water is supplied by pumping directly
and the pumps and distribution system must be designed to meet the peak demand.
The effect of monthly variation influences the design of storage reservoirs and
the hourly variations influences the design of pumps and service reservoirs. As
the population decreases, the fluctuation rate increases.

Maximum daily demand = 1.8 x average daily demand

Maximum hourly demand of maximum day i.e. Peak demand

= 1.5 x average hourly demand
= 1.5 x Maximum daily demand/24
= 1.5 x (1.8 x average daily demand)/24
= 2.7 x average daily demand/24
= 2.7 x annual average hourly demand

Design Periods & Population Forecast

This quantity should be worked out with due provision for the estimated
requirements of the future. The future period for which a provision is made in the
water supply scheme is known as the design period.

Design period is estimated based on the following:

 Useful life of the component, considering obsolescence, wear, tear, etc.

 Expandability aspect.
 Anticipated rate of growth of population, including industrial, commercial
developments & migration-immigration.
 Available resources.
 Performance of the system during initial period.