RAIN WATER HARVESTING 2024-

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RAIN WATER
HARVESTING 1
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Aknowledgement

The rapid development of cities and consequent

population explosion in urban areas has led to depletion
of surface water resources. For fulfillment of daily water
requirement, indiscriminate pumping of ground water is
being resorted to, leading to lowering of ground water
table. At the same time the rain water is not being
conserved which ultimately goes waste. To avoid this
imbalance, conservation of rain water in the form of rain
water harvesting is the only solution.
Rain water harvesting can be effectively
implemented in our office and residential complexes for
conservation of rain water. The subject has assumed lot
of significance in the present scenario. This has been
included in Indian Railway Works Manual 2000 vide
correction slip no. 10 dated 17.02.05 also. This
publication is an attempt to compile all the relevant
information regarding various methods commonly in use.
These methods can be used by field engineers for
designing and implementing Rain Water Harvesting
systems.
Efforts have been made to make the book more
useful for the field engineers. In this effort, the IRICEN
staff and faculty have contributed immensely, notably
among them are Mrs. Gayatri Nayak and Shri Sunil
Pophale. I am particularly thankful to Shri N.C. Sharda,
Senior Professor/Works for his valuable suggestions and
proof checking and Shri Praveen Kumar,
Professor/Computers for providing logistic assistance for
printing of the book.
Above all, the author is grateful to Shri Shiv Kumar,
Director, IRICEN for his encouragement and suggestions
for improving the publication.
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INDEX

CHAPTER-1 GENERAL 9 - 19
1.0 Introduction
1.1 Hydrologic cycle
1.2 Advantages of Rainwater
1.3 Rainwater harvesting
1.4 Advantages of Rainwater Harvesting
1.5 From where to Harvest Rainwater
1.6 Rainwater harvesting potential
1.7 Factors affecting run off from catchment
1.8 Important points relating to water storage and
recharging

CHAPTER-2 METHODS OF HARVESTING RAIN WATER

20-42
2.1 Rain water harvesting methods
2.1.1 Storing rain water for direct use
2.1.2 Recharging ground water aquifers from roof
top
runoff
2.1.3 Recharging ground water aquifers with runoff
from
ground areas
2.1.4 Modular Rain Water Harvesting System
2.2 Components of rain water harvesting
2.2.1 Catchment area
2.2.2 Coarse mesh/leaf screen
2.2.3 Gutter
2.2.4 Down spout/Conduit
2.2.5 First flushing device
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2.2.6 Filter
2.2.6.1 Sand Filter
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2.2.6.2 Charcoal Water Filter

2.2.6.3 Dewas Filter
2.2.6.4 Varun
2.2.6.5 Horizontal roughening filter and slow sand
filter
2.2.6.6 Rain water Purification Center
2.2.7 Settlement tank
2.2.8 Storage tank
2.2.8.1 Matching the capacity of the tank with the
area of the roof
2.2.8.2 Matching the capacity of the tank with the
quantity of water required by its users
2.2.8.3 Choosing a tank size, appropriate in terms of
cost, resources and construcgtion methods

CHAPTER-3 RECHARGING SUBSURFACE AQUIFERS

43 - 51
3.1 Methods of recharging subsurface aquifers
3.1.1 Through recharge pit
3.1.2 Recharge through abandoned hand pump
3.1.3 Recharge through abandoned dug well/ open
well
3.1.4 Through recharge trench
3.1.5 Recharge through shafts
3.1.6 Recharge trench with bore

CHAPTER-4 CASE STUDY 52 - 56

4.1 Introduction
4.2 Rain water harvesting at IRICEN hostel

CHAPTER-5 QUALITY OF WATER 57 - 63

REFERENCES 64
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GENERAL

It is said that “If third world war take places it will

be on water”. Already so many water disputes are going
on in our country between neighboring states for sharing
river water. Same situation of sharing river water also
exists with neighboring countries like Pakistan, Nepal
and Bangladesh. The basic reason of all these disputes is
scarcity of water and increasing requirement for human
consumption as well as for industrialization.
We, the human beings, are largely dependent on
water for our survival. Although water is as important for
survival of human beings as is food, air etc. but we
hardly pay any attention for its economical use and
conservation of this precious resource. This is resulting in
scarcity of water.
Due to indiscriminate pumping of ground water, the
water table has already gone down abnormally in many
parts of our country and if we do not wake up even now,
then our future generations may have to face severe
crisis of water.
In Delhi the water level in 1960 was, by and large,
within 4 to 5 m from ground level but by 2001 it has
gone down by 2-6 m in alluvial areas, 8-20 in south west
district and 8-30 in south district. Due to rapid
urbanization and indiscriminate pumping ground water
table has gone very deep and due to high content of
soluble solid, it has become un-potable in many area.
The rains are important source of water and if we
can harvest rain water, the scarcity of water can be
6

eliminated upto large extent. A major portion of rainwater

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that falls on earth surface runoff from stream to river to

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sea. On average only 8% of total rainfall recharges

ground aquifers. This can be enhanced upto 50% with
proper rainwater harvesting. Therefore, it is our bounden
duty to conserve the rain water in the form of rain water
harvesting.

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Few basic facts we should know:

• Only 3% of water on earth is available for human
use.
• Only 10% rain water is harvested currently. This
can be enhanced to 50% if adopted as habit or
movement. This can solve water problems of
major part of country.
• On an average rains, occur only for about 100
hours
every year.
Legislation on Rain Water Harvesting in India
• Under the sec 15 of Environment (protection)
Act 1986 central ground water authority
(ministry of water resources) has made
mandatory to adopt rain water harvesting
system for certain types of buildings /
institutions located in specified regions of
national capital territory.
• Ministry of Environment & forest (Govt. of India)
has circulated draft Gazette Nomination
regarding RWH in hilly area of entire country.
• New Delhi - MOUD has made RWH mandatory
since
June 2001 if roof area = 100sqm or plot area =
1000sqm.
• Mumbai: RWH mandatory since Oct 2002 for
new
buildings with area = 1000 sqm.
• Chennai: RWH has been made mandatory in all
new
buildings of three or more storeys.
• Hyderabad: RWH made mandatory since June 2001
if
area = 300 sqm.
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• Kanpur : RWH made mandatory for new buildings

with
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area = 1000 sqm.

• Indore :
– RWH made mandatory for new buildings if area
= 250 sqm.
– Rebate of 6% in property tax as incentive for RWH.
• Rajasthan: RWH made mandatory for new buildings
in
urban areas if plot area = 500 sqm.
• Haryana:

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– HUDA has made RWH mandatory for new buildings

in
urban areas irrespective of area.
– CGWA has asked all institutions and residential
buildings in notified areas of Gurgaon and
adjacent industrial areas to go for RWH.
Ministry of Railways (Railway board vide their letter
dated 2013/LMB/9/1 dtd 09-9-2013 has issued
policy instruction to adopt Rain water
harvesting systems have been made mandatory
in construction of all builtup assets. Indian
Railways water policy -2017 also reiterates this
policy.
1.0 Introduction
Water is the most common or major substance on
earth, covering more than 70% of the planet’s surface.
All living things consist mostly of water. For example, the
human body is about two third water. World wide
distribution of water is given in table
1.1 of the total volume of water, only 2 percent (over
28,000,000 Km3) is fresh water, which can be used
for consumption and for agriculture as given in table
1.2. The average runoff in the river system of India has
been assessed as 1869 km3, of this, the utilizable
portion by conventional storage and diversion is
estimated as about 690 km3. In addition, there is
substantial replenishable ground water potential in the
country estimated at 432 km3. The per capita availability
of water at the national level has reduced from about
5,177 m3 in the year 1951 to the present level of 1,869
m3. For improving per capita water availability in the
country, replenishment of ground water resources is a
necessity which can be done very effectively through
rain water harvesting.
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Table 1.1 World-wide distribution of water

S Water Type Volume Percentage

N (1000km3) of total
Global
Volume
1 Ocean 1,370,323 94.200
2 Ground water 60,000 4.100
(fresh & saline)
3 Glaciers 24,000 1.650
4 Lakes and 280 0.019
reservoirs
5 Soil moisture 85 0.006
6 Atmospheric water 14 0.001
7 River water 1.2 0.001
Total 1,454,703.2 100.000

Table 1.2 World-wide distribution of fresh water

SN Water Type Volume Percentage

(1000km3) of total
Global
Volume
1 Glaciers 24,000 85.000
2 Ground water 4,000 14.000
3 Lakes 155 0.600
and
reservoir
s
4 Soil moisture 83 0.300
5 Atmospheric 14 0.050
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water
6 River water 1.2 0.004
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Total 28,253.2 100.00

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Rain Water Harvesting:

The concept of rain water harvesting means
“Collecting Rain water when and wherever it falls for
future use”...It is just like “bank account where you
deposit the money when it is surplus & with draw when it
is deficient”.
Rain water harvesting is the technique of collection
& storage of rainwater at surface or in subsurface
acquifers. As most of rainfall water goes waste in form of
surface run off to stream, river and sea, simple
technique need to be developed to collect and store this
water in storage tank or direct this water to recharge
ground water acquifers (water bearing strata) to be
tapped later on for use in dry periods.
1.1 Hydrologic Cycle
The never-ending exchange of water from the
atmosphere to the oceans and back is known as the
hydrologic cycle (Fig. 1.1). This cycle is the source of all
forms of precipitation (hail, rain, sleet, and snow), and
thus of all the water.

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Fig. 1.1 Hydrologic cycle

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Precipitation stored in streams, lakes and soil

evaporates while water stored in plants transpires to
form clouds which store the water in the atmosphere.

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Currently, about 75% to 80% of conventional water

supply is from lakes, rivers and wells. Making the most
efficient use of these limited and precious resources is
essential. Otherwise, scarcity of water will be faced by
our future generations.
1.2 Advantages of Rain Water
The rain water’s environmental advantage and
purity over other water options makes it the first choice,
even though the precipitation cycle may fluctuate from
year to year.
a. Environmental Advantage
Collecting the rain that falls on a building and using
the same for various purposes is a simple concept. Since
the rain you harvest is independent of any centralized
system, you are promoting self- sufficiency and helping
to foster an appreciation for this essential and precious
resource. The collection of rain water not only leads to
conservation of water but also energy since the energy
input required to operate a centralized water system
designed to treat and pump water over a vast service
area is bypassed. Rain water harvesting also lessens
local erosion and flooding caused by runoff from
impervious cover such as pavement and roofs.
b. Qualitative Advantage
A compelling advantage of rain water over other
water sources is that it is one of the purest sources of
water available. Indeed, the quality of rain water is an
overriding incentive for people to choose rain water as
their primary water source, or for specific uses such as
watering houseplants and gardens. Rain water quality
almost always exceeds that of ground or surface water
as it does not come into contact with soil and rocks
where it dissolves salts and minerals and it is not
exposed to many of the pollutants that often are
discharged into surface waters such as rivers, and can
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contaminate groundwater. Rain water’s purity also

makes it an attractive water source for certain industries
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for which pure water is a requirement.

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1.3 Rain Water Harvesting

For our water requirement we entirely depend upon
rivers, lakes and ground water. However rain is the
ultimate source that feeds all these sources. Rain water
harvesting means to make optimum use of rain water at
the place where it falls i.e. conserve it

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and not allow to drain away and cause floods elsewhere.

The rain water harvesting may be defined as the
technique of collection and storage of rain water at
surface or in sub-surface aquifer before it is lost as
surface run off.
1.4 Advantages of Rain Water Harvesting
(a) Promotes adequacy of underground water
(b) Mitigates the effect of drought
(c) Reduces soil erosion as surface run-off is reduced
(d) Decreases load on storm water disposal system
(e) Reduces flood hazards
(f) Improves ground water quality / decreases
salinity (by dilution)
(g) Prevents ingress of sea water in subsurface
aquifers in
coastal areas
(h) Improves ground water table, thus saving
energy (to lift water)
(i) The cost of recharging subsurface aquifer is lower
than
surface reservoirs
(j) The subsurface aquifer also serves as storage
and
distribution system
(k) No land is wasted for storage purpose and no
population
displacement is involved
(l) Storing water underground is environment friendly
(m) Rainwater is bacteriological pure, free from
organic
matter and soft in nature
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(n) Rainwater can be harnessed at place of need &

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time of
need

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(o) Recharged aquifers also serve as distribution

system & water can be harnessed by just
putting a hand pump at convenient location
(p) The infrastructure required for rainwater
harvesting are simple & economical.

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1.5 From Where to Harvest Rain Water

i. Roof top to storage tank or Ground water
recharging point
ii. Unpaved area direct seepage to ground water
iii. Water bodies like ponds, tanks and lakes
iv. Storm water drains directed to recharge ground
water
1.6 Rain Water Harvesting Potential
The total amount of water that is received in the
form of rainfall over an area is called the rain water
endowment of that area. Out of this, the amount that can
be effectively harvested is called rain water harvesting
potential.
All the water which is falling over an area cannot be
effectively harvested, due to various losses on account of
evaporation, spillage etc. Because of these factors, the
quantity of rain water which can effectively be harvested
is always less than the rain water endowment. The
collection efficiency is mainly dependent on factors like
runoff coefficient and first flush wastage etc.
Runoff is the term applied to the water that flows
away from catchments after falling on its surface in the
form of rain. Runoff from a particular area is dependent
on various factors i.e. rainfall pattern and quantity,
catchment area characteristics etc. For determining
rainfall quantity, the rainfall data preferably for a period
of at least 10 years is required. This data can be
collected from meteorological department.
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Area of catchment x Amount of rainfall = Rain water

endowment
For determining the pattern of rainfall, the information may
be collected either from meteorological department or
locally.

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The pattern of rainfall in a particular catchment area

influence the design of rain water harvesting system. In
areas where rainfall is more but limited to very short
period in a year, big storage tanks would be required to
store rain water, if we are collecting rain water in storage
tanks for direct use. In such areas, it is preferable to use
rain water for recharging of ground water aquifers, if
feasible, to reduce the cost of rain water harvesting
system.
1.7 Factors Affecting Run Off from Catchment
i. Rainfall - quantity, pattern, intensity & duration
High intensity in less duration may get same
quantity but may get wasted due to high
surface run off due to less infiltration capacity
whereas mild rainfall with long duration will help
in recharging ground water.
ii. Catchment area characteristic
Unpaved surface have greater capacity of
retaining rain water & similarly green patches of
grass can retain large proportion of rainwater.
Runoff depends upon the area and type as well
as surface of catchment over which it falls as
well as surface features. Runoff can be
generated from both paved and unpaved
catchment areas.
Paved surfaces have a greater capacity of retaining
water on the surface and runoff from unpaved surface is
less in comparison to paved surface. In all calculations
for runoff estimation, runoff coefficient is used to account
for losses due to spillage, leakage, infiltrations
catchment surface wetting and evaporation, which will
ultimately result into reduced runoff. Runoff coefficient
for any catchment is the ratio of the volume of water
that run off a surface to the total volume of rainfall on
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the surface. The runoff coefficient for various surfaces is

given in table 1.3.
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Table 1.3 Runoff coefficients for various surfaces

S. Type of catchment Roof Coefficients

No. catchments
1 Tiles 0.8 - 0.9
2 Corrugated metal sheets 0.7 - 0.9
Ground surface coverings
3 Concrete 0.6 - 0.8
4 Brick pavement Untreated 0.5 - 0.6
ground
Catchments
5 Soil on slopes less than 10% 0.0 - 0.3
6 Rocky natural catchments 0.2 - 0.5
Source: Pacey, Amold and Cullis, Adrian 1989, Rain
water Harvesting: The collection of rainfall and runoff in
rural areas, Intermediate Technology Publications,
London pg-55.
Based on the above factors, the water harvesting
potential of site could be estimated using the following
equation:
Rain Water harvesting potential = Amount of
Rainfall x Area of catchment x Runoff coefficient The
calculation for runoff can be illustrated using the
following example:
Consider a building with flat terrace area (A) of 100
sqm located in Delhi. The average annual rainfall (R) in
Delhi is approximately 611mm. The runoff coefficient (C)
for a flat terrace may be considered as 0.85.
Annual water harvesting potential from 100
=AxRxC
= 100 x 0.611 x 0.85
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= 51.935 cum,
i.e. 51,935 liters
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1.8 Important Points Relating to Water Storage and

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Recharging
i. It is estimated that only 10 to 25% of rain water is
utilized to charged ground water but artificially with
rain water harvesting, it can be charged upto 50%
(para 2.6.3 of manual

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of rain water harvesting & conservation - Govt of India)

ii. Settlement tank need to be constructed in area. This
helps in two ways, it arrest silt & floating impurities
and secondly allow standing water to percolate in to
soil to finally recharge ground water. Apart from the
removing silt from desilting chamber, it act like a
buffer in case of excess rain fall to arrest surface run
off & store excess water. Its size can be decided on
the basis of size of catchment, intensity of rain fall &
rate of recharge depend on geological data like
porosity, permeability etc of area.



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METHODS OF HARVESTING RAIN

WATER

2.1 Rain Water Harvesting Methods

There are three methods of harvesting rain water as
given below:
(a) Storing rain water for direct use (Fig. 2.1)
(b) Recharging ground water aquifers, from roof top
run off (Fig. 2.2)
(c) Recharging ground water aquifers with runoff
from ground area (Fig. 2.3)
2.1.1 Storing rain water for direct use
In place where the rains occur throughout the year,
rain water can be stored in tanks (Fig. 2.1). However, at
places where rains are for 2 to 3 months, huge volume of
storage tanks would have to be provided. In such places,
it will be more appropriate to use rain water to recharge
ground water aquifers rather than to go for storage. If
the strata is impermeable, then storing rain water in
storage tanks for direct use is a better.
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Fig. 2.1 Storing rain water for direct use method.

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Similarly, if the ground water is saline/unfit for

human consumption or ground water table is very deep,
this method of rain water harvesting is preferable.
2.1.2. Recharging ground water aquifers from roof top run off
Rain water that is collected on the roof top of the
building may be diverted by drain pipes to a filtration
tank (for bore well, through settlement tank) from which
it flows into the recharge well, as shown in Fig.2.2. The
recharge well should preferably be shallower than the
water table. This method of rain water harvesting is
preferable in the areas where the rainfall occurs only for
a short period in a year and water table is at a shallow
depth. The various methods of recharging ground water
aquifers from roof top runoff are discussed separately in
Chapter 3.

Fig. 2.2 Recharging ground water aquifers from roof top run
off.
2.1.3 Recharging ground water aquifers with runoff from
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ground areas
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The rain water that is collected from the open

areas may be diverted by drain pipes to a recharge dug
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well / bore well through filter tanks as shown in Fig.2.3.

The abandoned bore well/dug well can be used cost
effectively for this purpose. The various methods

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of recharging ground water aquifers with runoff from ground

areas
are discussed separately in Chapter 3.

Fig. 2.3 Recharging ground water aquifers with runoff from

ground areas.
2.1.4 Modular Rain Water Harvesting System
Modular Tank System is a subsurface water
infiltration storage for storm water control and
management system and hence known as modular rain
water storage harvesting system and subsoil drainage It
is efficient, cost effective and ecologically sustainable.
Its main function of modular tank is to allow on site
natural water infiltration and this prevents surface runoff.
This underground system is best suited for flat ground
area for rainwater harvesting and storm water
management.
This system can be used to hold any volume of
water. These systems are built out of modular plastic
cubes. They are arranged to appropriate sizes, then
wrapped in a liner and covered with soil and GI sheets.
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This allows the storm water to be managed underground

and can be easily integrated into landscaping. This helps
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in creating load bearing void spaces for underground

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water storage. Modular boxes are made up of recycled

plastics. These modules are 95 percent voids and are
strong enough for vehicular traffic and parking.

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Runoff water from surface and roof tops would

be channelized to filteration unit. Filteration unit should
consist of :
1) Sedimentation tank
2) Filteration through microfilters of FRP tank and
similar
arrangemets
3) Sand filter with geotextile layer at the top.

Water would then be taken to modular rain water storage

or similar arrangement as per site feasibility. (Fig. 2.4 (a),
(b), (c))

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Fig. 2.4 (a)

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Fig. 2.4 (b)

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Fig. 2.4 (c)

Courtesy: CPWD Rainwater Harvesting and Conservation
Manual 2019
32

2.2 Components of Rain Water Harvesting

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The rain water harvesting system consists of following

basic components –
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(a) Catchment area

(b) Coarse mesh / leaf screen
(c) Gutter
(d) Down spout or conduit
(e) First flushing device
(f) Filter
(g) Storage tank
(h) Recharge structure
2.2.1 Catchment area
The catchment area is the surface on which the
rain water falls. This may be a roof top or open area
around the building. The quality of water collected from
roof top is comparatively much better than collection
from the ground. Rain water harvested from catchment
surfaces along the ground should be used for lawn
watering, flushing etc., because of increased risk of
contamination. This water can also be used for
recharging ground aquifers after proper filtration.
The rain water yield varies with the size and
texture of the catchment area. A smooth, cleaner and
more improvised roofing material contributes to better
water quality and greater quantity with higher value of
runoff coefficient. (refer table 1.3 for runoff coefficient)
When roof of the house is used as the catchment
for collecting the rain water, the type of roof and the
construction material affect the runoff coefficient and
quality of collected water. Roofs made of RCC, GI
sheets, corrugated sheets, tiles etc. are preferable for
roof top collection. But thatched roofs are not preferred
as these add colour and dissolved impurities to water.
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Water to be used for drinking purpose should not be

collected from roof with damaged AC sheets or from
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roofs covered with asphalt and lead flashing or lead

based paints as the lead contamination may occur in the
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collected water.

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2.2.2 Coarse mesh / leaf screen

To prevent the entry of leaves and other debris in
the system, the coarse mesh should be provided at the
mouth of inflow pipe for flat roofs as shown in Fig. 2.5.

Fig. 2.5 Coarse mesh

For slope in roofs where gutters are provided to
collect and divert the rain water to downspout or
conduits, the gutters should have a continuous leaf
screen, made of ¼ inch wire mesh in a metal frame,
installed along their entire length, and a screen or wire
basket at the head of the downspout (Fig. 2.6).
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Fig. 2.6 Leaf screen

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2.2.3 Gutter
Gutter is required to be used for collecting water
from sloping roof and to divert it to downspout. These
are the channels all around the edge of a sloping roof
to collect and transport rain water to the storage tank.
Gutters can be of semi-circular, rectangular or
trapezoidal shape. Gutters must be properly sized,
sloped and installed in order to maximize the quantity of
harvested rain. Gutter can be made using any of the
following materials:
(a) Galvanized iron sheet
(b) Aluminum sheet
(c) Semi-circular gutters of PVC material which can
be readily prepared by cutting these pipes into
two equal semicircular channels
(d) Bamboo or betel trunks cut vertically in half (for
low cost housing projects )
The size of the gutter should be according to the
flow during the highest intensity rain. The capacity of the
gutters should be 10 to 15% higher. The gutters should
be supported properly so that they do not sag or fall off
when loaded with water. The connection of gutters and
down spouts should be done very carefully to avoid any
leakage of water and to maximize the yield. For jointing
of gutters, the lead based materials should not be used,
as it will affect the quality of water.
2.2.4 Down spout / conduit
The rain water collected on the roof top is
transported down to storage facility through down spouts
/ conduits. Conduits can be of any material like PVC, GI
or cast iron. The conduits should be free of lead and any
other treatment which could contaminate the water.
37

Table 2.1 gives an idea about the diameter of pipe

required for draining out rain water based on rainfall
Page

intensity and roof area.

RAIN WATER HARVESTING 2024-
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Table 2.1 Sizing of Rainwater pipes for Roof Drainage in mm/

hr.

Roof area in sq.m for Average rate of rain fall

Diameter of

(in mm/hr)
pipe (in

50 75 100 125 150 200

mm)

50 29.70 19.80 14.85 11.88 9.90 7.42

65 57.23 38.15 28.61 22.89 19.08 14.31
75 81.84 54.56 40.92 32.74 27.28 20.46
100 168 112 84 67.20 56 42
125 293.48 195.66 146.74 117.39 97.83 73.37
150 462.95 308.64 231.48 185.18 154.32 115.74
Note: For Rainwater pipes of other materials, the Roof area shall
be multiplied by (0.013/co-efficient of roughness of surface of
that material)
Source: National Building Code -2016
2.2.5 First flushing device
Roof washing or the collection and disposal of the
first flush of water from a roof, is very important if the
collected rain water is to be used directly for human
consumption. All the debris, dirt and other contaminants
especially bird dropping etc. accumulated on the roof
during dry season are washed by the first rain and if this
water will enter into storage tank or recharge system it
will contaminate the water. Therefore, to avoid this
contamination a first flush system is incorporated in the
roof top rain water harvesting system. The first flushing
device, dispose off the first spell of rain water so that it
does not enter the system. If the roof is of sloping type,
then the simplest system consists of a pipe and a gutter
down spout located ahead of the down spout from the
gutter to the storage tank. (Fig. 2.7)
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Fig. 2.7 First flushing device

The pipe is usually 6 or 8 inch PVC pipe which has a
valve and cleanout at the bottom, most of these devices
extend from the gutter to the ground where they are
supported. The gutter down spout and top of the pipe
are fitted and sealed so that water will not flow out of the
top. Once the pipe has filled, the rest of the water flows
to the downspout connected to storage tank. The
alternate scheme for sloping roof is shown in Fig. 2.8.
This involves a very simple device which is required
to be operated manually. In down take pipe at the
bottom one plug/ valve is provided. When the rainy
season start, this plug should be removed, and initial
collection of roof top water should be allowed to drain.
After 15 – 20 minutes, plug / valve should be closed so
that collected rain water can be diverted to storage tank.
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Fig. 2.8 First flushing device.

2.2.6 Filter
If the collected water from roof top is to be used for
human consumption directly, a filter unit is required to
be installed in RWH system before storage tank. The
filter is used to remove suspended pollutants from rain
water collected over roof. The filter unit is basically a
chamber filled with filtering media such as fiber, coarse
40

sand and gravel layers to remove debris and dirt from

water before it enters the storage tank. The filter unit
Page

should be placed after first flush device but before

storage tank. There are various type of filters which have
RAIN WATER HARVESTING 2024-
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been developed all over the

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country. The type and selection of filters is governed by

the final use of harvested rain water and economy.
Depending upon the filtering media used and its
arrangements, various types of filters available are
described below.
2.2.6.1 Sand filter
In the sand filters, the main filtering media is
commonly available sand sandwitched between two
layers of gravels. The filter can be constructed in a
galvanized iron or ferro cement tank. This is a simple
type of filter which is easy to construct and maintain. The
sand fillers are very effective in removing turbidity,
colour and microorganism. In a simple sand filter that
can be constructed domestically, filter media are placed
as shown in Fig. 2.9.

Fig. 2.9 Sand filter

2.2.6.2 Charcoal water filter
This is almost similar to sand filter except that a
10-15 cm thick charcoal layer placed above the sand
layer. Charcoal layer inside the filter result into better
filtration and purification of water. The commonly used
42

charcoal water filter is shown in Fig. 2.10.

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RAIN WATER HARVESTING 2024-
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Fig. 2.10 Charcoal water filter

2.2.6.3 Dewas filter
This filter was developed by officials of Rural
Engineering Services of Dewas. In Dewas, the main
source of water supply is wells which are used to extract
ground water for supply of water. Because of regular
extraction of ground water, the water table is going
down rapidly. To recharge the ground water, all the
water collected from the roof top is collected and passed
through a filter system called the Dewas filter( Fig. 2.11).
The filtered water is finally put into service tube well for
recharging the well.
The filter consists of a PVC pipe 140mm in
diameter and 1.2m long. There are three chambers. The
first purification chamber has pebbles of size varying
between 2-6 mm, the second chamber has slightly larger
pebbles between 6 to 12 mm and the third chamber has
largest 12 – 20mm pebbles. There is a mesh on the out
flow side, through which clean water flows out after
passing through the three chambers. This is one of the
most popular filter type being used in RWH systems.
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Fig. 2.11 Dewas filter

2.2.6.4 Varun
This filter has been developed by Shri S. Viswanath,
a Bangalore based water harvesting expert. “Varun” is
made from 90 lit. High Density Poly Ethylene (HDPE)
drum. The lid is turned over and holes are punched in it.(
Fig. 2.11) The punched lid acts as a sieve which keeps
out large leaves, twigs etc. Rain water coming out of the
lid sieve then passes through three layers of sponge and
150mm thick layer of coarse sand. Because of sponge
layers, the cleaning of filter becomes very easy. The
first layer of sponge can be removed and cleaned very
easily in a bucket of water. Because of the layers of
sponge, the sand layer does not get contaminated and
does not require any back washing / cleaning. This filter
can handle about 50mm per hour intensity rain fall from
a 50 sqm roof area.
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RAIN WATER HARVESTING 2024-
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Fig. 2.12 Varun

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2.2.6.5 Horizontal roughening filter and slow sand filter

This is one of the most effective filter for
purification of water being used in coastal areas of
Orissa. The horizontal roughening filter (HRF) acts as a
physical filter and is applied to retain solid matter, while
slow sand filter (SSF) is primarily a biological filter, used
to kill microbes in the water. The water is first passed
through the HRF and then through SSF.
The HRF usually consists of filter material like
gravel and coarse sand that successively decrease in
size from 25mm to 4mm. The bulk of solids in the
incoming water is separated by this coarse filter media
or HRF. The filter channel consists of three uniform
compartments, the first packed with broken bricks, the
second with coarse sand followed by fine sand in the
third compartment. At every outlet and inlet point of the
channel, fine graded mesh is implanted to prevent entry
of finer material into the sump. The length of each
channel varies accordingly to the nature of the site
selected for the sump (Fig. 2.13).

46

Fig. 2.13 Horizontal roughening filter and slow sand filter

The slow sand filter (SSF) consists of fine sand in a
Page

channel of size one sqm in cross section and eight metre

in length, laid across the tank embankment. The water
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after passing through SSF is stored in a sump. From this

sump water can be supplied through pipe line or can be
extracted through hand pump.

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RAIN WATER HARVESTING 2024-
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Wherever the roof top area is very large, the filters

of high capacity are designed to take care of excess flow.
For large roof tops, a system is designed with three
concentric circular chambers in which outer chamber is
filled with sand, the middle one with coarse aggregate
and the inner most layer with pebbles (Fig. 2.14). Since
the sand is provided in outer chamber, the area of
filtration is increased for sand, in comparison to coarse
aggregate and pebbles. Rain water reaches the center
core and is collected in the sump where it is treated with
few tablets of chlorine and is made ready for
consumption.

48

Fig. 2.14 Filter for large roof top

2.2.6.6 Rain water purification center
Page

This filter has been developed by three

RAIN WATER HARVESTING 2024-
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Netherlands based companies for conversion of rain

water to drinking water and is popularly known as Rain
PC. Rain PC is made of ultra violet

49
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RAIN WATER HARVESTING 2024-
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resistant poly-ethylene housing and cover, stainless steel

rods and bolts, a nickel-brass valve and an adapter for
maintaining constant volume (Fig. 2.15).
This filter can effectively remove E-coli and other
bacteria from water using Xenotex-A and active carbon
cartridges along with ultra membrane filtration modules.
This filter is easy to operate and maintain and needs no
power. This operates at low gravity pressure and
maintains nearly constant volume irrespective of water
pressure. The system is capable of providing a constant
flow of about 40 lit. of rain water per hour. The Xenotex-
A and activated carbon cartridges processes up to
20,000 liters of water and can be regenerated up to 10
times.

Fig. 2.15 Rain water purification center

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2.2.7 Settlement tank

If the collected rain water from roof top / ground
is used to recharge ground water reserve, it should be
passed through a desilting pit/ settlement tank before
entering the aquifer. The settlement tank facilitates the
settling down of suspended material
i.e. silt and other floating impurities before the water
recharge the aquifer. The settlement tank should have
inlet, outlet and overflow device. Any container with
adequate capacity of storage can be used as settlement
tank. It can be either underground or over ground.
The settlement tank acts like a buffer in the
system. In case of excess rainfall, the rate of recharge,
especially of borewells, may not match the rate of
rainfall. In such situations, the desilting chamber holds
the excess amount of rain water, till it is soaked by
recharge structures. The settlement tank can be
prefabricated PVC or Ferro-cement tanks, masonry and
concrete tanks (Fig. 2.16). In case of underground
settlement tank, the bottom can be unpaved surface so
that water can percolate through soil.

51

Fig. 2.16 Settlement tank

Page

For designing the optimum capacity of the

RAIN WATER HARVESTING 2024-
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settlement tank, the following parameters need to be

considered –
(a) Size of the catchment
(b) Intensity of rain fall

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RAIN WATER HARVESTING 2024-
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(c) Rate of recharge

The capacity of the tank should be enough to retain
the runoff occurring from conditions of peak rainfall
intensity. The rate of recharge in comparison to runoff is
a critical factor. The capacity of recharge tank is
designed to retain runoff from at least 15 minutes of
rainfall of peak intensity.
For example, for Delhi peak hourly rainfall is 90mm
(based on 25 year frequency) and 15 minutes peak
rainfall is 22.5 mm say 25mm.
Area of roof top catchment (A) = 100 sqm.
Peak rain fall in 15 min (r) = 25mm
(0.025m) Runoff coefficient (C) = 0.85
Then, capacity of settlement tank = A x r x C
= 100 x 0.025 x 0.85
= 2.125 cum
or 2,125 liters
2.2.8 Storage tank
Whenever the rain water collected from roof top is
used directly for various purposes, storage tank is
required. The storage tank can be cylindrical, rectangular
or square in shape. The material of construction can be
RCC, ferrocement, masonry, PVC or metal sheets.
Depending upon the availability of space, the storage
tank can be above ground, partially underground or fully
underground. The design of storage tank is dependent
on many factors which are listed below:
(a) Number of persons in the household – The greater the
number of persons, more will be requirement of
53

water.
(b) Per capita requirement – varies from household
Page

to household, based on standard of living. The

requirement also varies with season. In summer
RAIN WATER HARVESTING 2024-
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the requirement is more in comparison to

winter. Similarly, the per capita requirement is
more in urban areas in comparison to rural
areas.

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RAIN WATER HARVESTING 2024-
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(c) Average annual rainfall.

(d) Rainfall pattern – It has a significant impact on
capacity of storage tank. If the rainfall is
uniformly spread throughout the year, the
requirement of storage capacity will be less. But
if the rainfall is concentrated to a limited period
in a year, the storage tanks of higher capacity
will be required.
(e) Type and size of catchment – Depending upon
the type of roofing material, the runoff
coefficient varies which affect the effective yield
from a catchment area. The size of the
catchment also has a bearing on tank size. The
more the catchment area, larger the size of
storage tank.
The design of the storage tank, can be done using following
three approaches:
(a) Matching the capacity of the tank to the area of the
roof.
(b) Matching the capacity of the tank to the quantity of
water
required by its users.
(c) Choosing a tank size that is appropriate in terms of
costs,
resources and construction methods.
2.2.8.1 Matching the capacity of the tank with the area of the
roof
In this approach, storage capacity of the tank is
determined, based on the actual catchment area and
total rain water harvesting potential. All the water
collected from roof top is stored in storage tank and
storage capacity is calculated based on the consumption
pattern and rainfall pattern.
55

Illustration – Suppose the storage tank has to be

Page

designed for 200 sqm roof area in Chennai area where

average annual rainfall is 1290mm. The runoff coefficient
RAIN WATER HARVESTING 2024-
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for roof top is 0.85, so for every 1mm rainfall, the

quantity of water which can be harvested is 200 x 0.001
x 0.85 = 0.170m3 or 170 liters.
The monthly consumption of water is 20,000 liters. Table
2.2 given below illustrates the method of calculation of
required storage capacity of the tank.

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Table 2.2 Calculation of capacity of storage tank

Demand in
fall in mm

be- tween (4)

Cumulative
Monthly Rain

Rain fall

Cumulative

Difference
Harvested in

harvested
Month

liters
rain fall

Monthly

& (6)
(1) (2) liters
(3) (4) (5) (6) (7)
July 98 16660 16660 20000 20000 -3340
Aug 136 23120 39780 20000 40000 -220
Sept. 122 20740 60520 20000 60000 520
Oct. 282 47940 108460 20000 80000 28460
Nov. 354 60180 168640 20000 100000 68640
Dec. 141 23970 192610 20000 120000 72610
Jan. 30 5100 197710 20000 140000 47710
Feb. 8 1360 199070 20000 160000 39070
Mar. 5 850 199920 20000 180000 39920
Apr. 15 2550 202470 20000 200000 2470
May 38 6460 208930 20000 220000 -11070
June 61 10370 219300 20000 240000 20700

Total annual rain fall: 1290mm

From the above table, it can be seen that
difference between cumulative rainfall harvested and
cumulative demand is maximum in the month of
December at 72610 liters. So the capacity of storage
tank should be 72610 liters, say 73000 liters.
2.2.8.2 Matching the capacity of the tank with the quantity of
water required by its users
Suppose the system has to be designed for meeting
drinking water requirement of a 4 member family living
in the building with a roof top area of 200 sqm. The
average annual rainfall in the Chennai region is 1290
57

mm. Daily drinking water requirement is 10 liters per

person.
Page

If area of catchment (A) = 200 sq.m.

RAIN WATER HARVESTING 2024-
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average annual rainfall ( R) = 1290 mm

(1.290 m) and runoff coefficient (C) = 0.85
Then, annual rain water
harvesting potential = 200 x 1.290 x 0.85
= 219.30 cum or 2,19,300 liters
The tank capacity is determined based on the dry
period
i.e. the period between the two consecutive rainy
seasons. For example, with a monsoon extending over 5
months, the dry season is of 215 days.
Drinking water requirement for the family during dry
season
= 215 x 4 x 10 = 8600 liters. After keeping some factor
of safety, the tank should have 20 percent more capacity
than required above, i.e. 10,320 liters.
2.2.8.3 Choosing a tank size, appropriate in terms of costs,
resources and construction methods.
In practice, the costs, resources and construction
methods tend to limit the storage tank to smaller
capacity in comparison to requirement as per approach 1
& 2. Depending upon the budget and space available,
the construction of storage tank is done so that at least
for some period dependence on municipal sources /
water tankers can be minimized.


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RECHARGING SUBSURFACE
AQUIFERS

3.1 Methods of Recharging Subsurface Aquifers

The various methods of recharging subsurface aquifers are:
1. Through recharge pit.
2. Recharge through abandoned hand pump.
3. Recharge through abandoned dug well/open well.
4. Through recharge trench.
5. Recharge through shaft.
6. Recharge trench with bore.
3.1.1 Through recharge pit
This method is suitable where permeable strata is
available at shallow depth. It is adopted for buildings
having roof area up to 100 sqm. Recharge pit of any
shape is constructed generally 1-2 m wide and 2-3 m
deep. The pit is filled with boulders, gravel and sand for
filtration of rain water. Water entering in to RWH
structure should be silt free. Top layer of sand of filter
should be cleaned periodically for better ingression of
rain water in to the sub soil. Details are shown in Fig. 3.1.
3.1.2 Recharge through abandoned hand pump
In this method, an abandoned hand pump is used
59

as recharging structure. It is suitable for building having

roof top area up to 150 sqm . Roof top rain water is fed
Page

to the hand pump through 100 mm dia. pipe as shown in

RAIN WATER HARVESTING 2024-
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Fig. 3.2. Water fed in the Rain water harvesting structure

should be silt free. Water from first

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RAIN WATER HARVESTING 2024-
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rain should be diverted to drain through suitable

arrangement. If
water is not clear then filter should be provided.
3.1.3 Recharge through abandoned dug well / open well
In this method, a dry / unused dug well can be used
as a recharge structure. It is suitable for buildings having
a roof top area more then 100 sqm . Recharge water is
guided through a pipe of 100 mm to the bottom of the
well as shown in Fig. 3.3. Well cleaning and desilting is
imperative before using it. Recharge water guided should
be silt free, otherwise filter should be provided as shown
in Fig. 3.3. Well should be cleaned periodically and
chlorinated to control bacteriological contamination.
3.1.4 Through recharge trench
This method is used where permeable strata is
available at shallow depth. It is suitable for buildings
having roof top area between 200 & 300 sqm. In this
method, trench of 0.5-1.0 m wide, 1-1.5 m deep and of
adequate length depending upon roof top area and
soil/subsoil characteristics should be constructed and
filled with boulders, gravel and sand as shown in Fig. 3.4.
Cleaning of filter media should be done periodically.
3.1.5 Recharge through shafts
This method is suitable where shallow aquifer is
located below clayey surface. It is used for buildings
having roof top area between 2000 & 5000 sqm.
Recharge shaft of diameter 0.5-3 m and 10-15 m deep is
excavated mechanically. The shaft should end in
permeable strata. The shaft should be filled with
boulders, gravel and sand for filtration of recharge water.
Top sand layer should be cleaned periodically.
Recharge shaft should be constructed 10-15 m away
61

from the buildings for the safety of the buildings. The

Page

details are given in Fig. 3.5.

3.1.6 Recharge trench with bore
RAIN WATER HARVESTING 2024-
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This method is used where sub-soil is impervious

and large quantity of roof water/ surface run off is
available. In this, trench is made 1.5-3 m wide and 10-30
m length depending upon water availability. Wells of
150-300 mm dia. and 3-5 m deep (below

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RAIN WATER HARVESTING 2024-
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pervious layer) are constructed in the trench. Numbers of

wells to be dug are decided in accordance to water
availability and rate of ingression. Trench is filled with
filtration media as shown in Fig.
3.6. A suitable silt chamber is also inserted with grating for
water
diverting arrangements as shown in the figure.

63

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Fig. 3.1 Through recharge pit

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RAIN WATER HARVESTING 2024-2025

Fig. 3.2 Recharge through abandoned hand pump

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RAIN WATER HARVESTING 2024-2025

Fig. 3.3 Recharge through abandoned open well

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RAIN WATER HARVESTING 2024-2025

67
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Fig. 3.4 Through recharge trench
RAIN WATER HARVESTING 2024-2025

68
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Fig. 3.5 Recharge through shaft
RAIN WATER HARVESTING 2024-2025

Fig. 3.6 Recharge trench with bore



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CASE STUDY

4.1 Introduction
The various method of rain water harvesting
explained in previous chapters are equally applicable for
the single building or structure which is having built up
area. Since the principals of rain water harvesting are
universal, the same can be applied for rain water
harvesting in big colonies/establishment with some
minor modifications. The basic components of any rain
water harvesting system remain the same but the
number and size may vary depending upon the
catchments area. If the rain water harvesting has to be
implemented in a large area i.e. an office complex or big
residential complex, the area can be subdivided into
smaller parts. The runoff from each smaller part can be
harvested through recharge structures constructed
nearby while the runoff from open areas can be
canalized through storm water drains into recharge
structures. Fig.4.1 given below indicates one such type of
scheme.
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Fig. 4.1 Rain water harvesting in a large area

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4.2 Rain Water Harvesting at IRICEN Hostel

The Indian Railways Institute of Civil Engineering
(IRICEN), Pune is having a 104 rooms hostel at Koregaon
Park. The total area of the hostel building is approx.
1162.5 sqm and open area in the hostel is approx. 900
sqm. In first phase, the rain water harvesting has been
implemented in left wing of the hostel, covering a roof
top area of 465 sqm and open area of 788 sqm.
For rain water harvesting, a deep bore well of 32m.
depth and 150mm dia. has been bored. The annual
rainfall (R) in Pune is approx. 700mm. Considering a roof
top area (A) of 465 sqm and runoff coefficient (C) of 0.85,
the rain water harvesting potential from roof top is
=AxRxC
= 465 x 0.700 x 0.85
= 276.675 cum or 2,76,675 liters
The open area from which runoff is to be collected
is approx. 788 sqm. Considering a runoff coefficient (C)
of 0.55 for open areas, the rain water harvesting
potential from open area is
=AxRxC
= 788 x 0.700 x 0.55
= 303.38 cu.m. or 3,03,380 liters
Total rain water harvesting potential annually is
5,80,055 liters from the roof top and open area. The
scheme for rain water harvesting implemented at IRICEN
is shown in fig 4.2.
The runoff from roof top is collected through down
take pipes / conduits of 100mm dia. After collection
through conduits, the collected water is channelised
72

through a network of drains (underground) having

Page

250/150mm dia. RCC pipes to a settlement tank cum

filter. Similarly the runoff from open area is also collected
RAIN WATER HARVESTING 2024-
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through series of chambers constructed along the drains

and channelised to settlement tank cum filter. The
details of settlement tank cum filter are shown in Fig.
4.3.

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74

Fig. 4.2 Rain water harvesting at IRICEN hostel

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RAIN WATER HARVESTING 2024-
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75

Fig. 4.3 Details of settlement tank / filter for Rain Water

Page

Harvesting
RAIN WATER HARVESTING 2024-
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The capacity of filter cum settlement tank is 8400

liters, which is sufficient to retain runoff from at least 15
minutes rainfall of peak intensity. After passing through
the filter media, the filtered water enters into the 150mm
dia 32m deep borewell, bored specifically for this
purpose i.e. for recharging ground water aquifer. The
overflow from settlement tank/filter enters into the
municipal sewer through the connection provided. The
total cost of implementation of the project in IRICEN
hostel was approximately Rs. 55,000 and the system was
implemented in January 2006.



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6
RAIN WATER HARVESTING 2024-
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QUALITY OF WATER

The rain water is one of purest form of water and

does not contain suspended / dissolved impurities.
However when this water is collected through rain water
harvesting, it gets contaminated because of contact with
roof surface/ground and some of the impurities get
mixed in it. These impurities are required to be removed
before collecting the harvested rain water in storage
tank or diverting it or recharging of ground water
aquifers.
Following precautions should be taken to ensure
quality of
water:
1. Roof over which water falls, should be cleaned
beforerain fall.
2. The suitable type of first flushing device to be
installedand initial 10 to 15 minutes of runoff should
be diverted.
3. The water collected from roof top only, should be
storedin storage tank for direct use.
4. The runoff from surface/ground should be preferably
beused for recharging ground water aquifers after
proper filtration.
5. The rain water collected from roof top should
77

passthrough suitable type of filter and only then it

should be stored in storage tank / used for
Page

recharging ground water aquifers.

The harvested rain water may contain some toxic
6
RAIN WATER HARVESTING 2024-
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substances which may affect our health. The water

collected from roof top after filtration can be used
directly for lawn watering, washing etc. But if this water
has to be used directly for drinking purpose, then quality
of water must be ascertained before use.
The water used for drinking should comply with
the

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6
RAIN WATER HARVESTING 2024-
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provisions of IS-10500:2012 i.e. Indian Standard

“DRINKING WATER – SPECIFICATION (First Revision)”.
The important test characteristics for drinking water as
given in Table 1 of IS10500:2012 are reproduced in Table
5.1 for ready reference.
To test the quality of water, the water samples can
be collected and testing can be done in testing
laboratories But as a routine, the quality of water
can also be checked with the help of testing kits by
the users themselves. In case, water is not potable,
treatment of water may be necessary to make it fit
for human consumption. For treatment of water, the
following measures can be taken at household level.
(a) Filtration of water should be done using suitable
type of filter. The details of various type of filter are
given in chapter 2.
(b) Chemical disinfection can be done by chlorination.
Chlorination is done with stabilized bleaching
powder, which is a mixture of chlorine and lime.
Chlorination can kill all types of bacteria and make
water safe for drinking purposes. Approx. 1 gm of
bleaching powder is sufficient to treat 200 liters of
water otherwise chlorine tablets, which are easily
available in the market can be used for disinfection
of water. One tablet of 0.5gm is enough to disinfect
20 litres of water.
(c) Boiling water is one of the effective method of
purification. Boiling water for 10 to 20 minutes is
enough to remove all biological contaminants.
79

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Table 5.1 Important test characteristics for drinking water

Permissible
Require-
Undesirable Limit in the
Substance ment Method of
SN Effect Outside Absence of Remarks
Characteristics (Acceptable Test (Ref. to
the Desirable Alternate
limit) IS)
Limit Source
Essential Characteristics
I Color, Hazen 5 Above 5. Consumer 15 3025 (Part- Extended to
units, Max. acceptance 4):193 25 only if
decreases toxic
substances
are not
59

suspected in
absence
of alternate
sources.
II Odour Agreeable - 3025 (Part-5): a) Test cold
1983 and when
heated b)
Test at
several
dilutions
III Taste Agreeable - Agreeable 3025 (Part Test to be

81
7&8): 1984 conducted
only after

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established.

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IV Turbidity NTU 1 Above 5, consumer 5 3025 (Part

Max. acceptance 10):
decreases. Beyond 1984
this range the
water will affect
the mucous
membrane and/or
water supply
system
V pH Value 6.5 to 8.5 Beyond this range No relaxation 3025 (Part
the water will affect 11):
the mucous 1984
60

membrane and/or
water supply
system
VI Total 200 Encrustation in 600 3025 (Part
Hardness (as water supply 12):
CaCO3) mg/l, structure and 1983
Max. adverse effect on
domestic use.
VII Iron (ad Fe) 0.3 Beyond this limit No relaxation 32 of 3025:
mg/l Max. taste/ appearance 1964
are affected, has

83
adverse effect on
domestic uses and

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water supply
structures, and
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promotes iron
bacteria.

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VIII Chloride (as 250 Beyond this limit, 1000 3025 (Part
Cl) mg/l, test corrosion and 32):
Max. 0.3 palatability are 1988
affected.
IX Residual 0.2 - - 1.0 3025 (Part To be
free * 26): applicable
chlorine * When 1986 only when
mg/l Min protectio water is
n against chlorinated.
viral Tested at
infection
consumer
is
required,i end. When
61

t should protection is
be required, it
minimum should be Min
0.5mg/l 0.5 mg/l
X Fluoride (as 1.0 Fluoride may be 1.5 23 of 3025
F) kept as low as 1964
mg/l Max. possible. High
fluoride may cause
fluorosis
XI Total 500 Beyond this 2000 3025 (Part
Dissolved palatability 16):

85
solid decreases and may 1984
cause gastro

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XII Calcium (as 75 Encrustation in 200 3028 (Part

Ca) mg/l water supply 40):
Max. structure and 1991
adverse effect on
domestic use
XIII Magnesium 30 Encrustation to 100 16.33.34 of IS
(as Mg) mg/l water supply 3025 1964
structure
and adverse effect
on domestic use
Astringent taste
will be caused
62

beyond this
discoloration and
corrosion of pipes,
fitting and
utensils.
XIV Copper (as 0.05 1.5 36 of 3025
Cu) mg/l Max. 1964
XV Sulphate 200 Beyond this causes 400 (sec. col 3025 (Part 24) Provided
(as SO4) gastro intestinal 7) 1986 Magnesium
irritation when (as Mg) does
magnesium or
not exceed

86
sodium are
present. 30 mg/l

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XVI Nitrate 45 Beyond this No relaxation 3025 (Part
(as NO2) methaemoglobinem 34):
RAIN WATER HARVESTING 2024-2025

mg/l ia takes place 1988

Max.

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XVII Cadmium (as 0.003 Beyond this, the No relaxation See Note 1 To be tested
Cd) mg/l Max. water becomes when pollution
toxic is suspected
XVIII Arsenic (as 0.01 Beyond this, the 0.05 3025 (Part To be tested
As) water becomes 37): when pollution
mg/l Max. toxic 1988 is
suspected
XIX Lead (as Pb) 5 Beyond this, the No relaxation See Note 1 To be tested
mg/l, Max. water becomes when pollution
toxic is suspected
XX Zinc (as Zn) 5 Beyond this limit it 15 39 of 3925 To be tested
mg/l, Max can cause 1964 when
astringent taste & pollution
an opalescence in
63

water
XXI Mineral 1.00 Beyond this limit No relaxation Gas To be tested
Oil mg/l, undesirable taste chromato- when pollution
Max. and odour after graphic is suspected.
chlorination method
take place.
Note-1: Atomic absorption spectrophotometric method may be used.

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References
1. Texas Guide on rain water harvesting
2. “A Water Harvesting Manual for urban areas” issued
by Centre For Science and Environment
3. Paper on “Rain Water Harvesting” written by Sri.
Kaushal Kishore, Materials Engineer, Roorkee
published in CE&CR , May 2004
4. Indian Standard Guidelines for Rain Water
Harvesting in hilly areas by roof water collection
system” IS 14961:2001
5. Indian Standard “ Drinking Water Specifications” IS
10500 :
2012
6. Indian Railway Works Manual 2000
7. CPWD Rainwater Harvesting and Conservation
Manual 2019
8. NBC-2016
9. www.rainwaterharvesting.org
10. www.aboutrainwaterharvesting.com

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