RAIN WATER HARVESTING

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3. Rainwater Harvesting
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4. The scarcity of water is a well-known fact. In spite of higher
average annual rainfall in India (1,170 mm, 46 inches) as
compared to the global average (800 mm, 32 inches) it does not
have sufficient water.
Most of the rain falling on the surface tends to flow away rapidly,
leaving very little for the recharge of groundwater. As a result,
most parts of India experience lack of water even for domestic
uses.
Surface water sources fail to meet the rising demands of water
supply in urban areas, groundwater reserves are being tapped and
over-exploited resulting into decline in groundwater levels and
deterioration of groundwater quality.
This precarious situation needs to be rectified by immediately
recharging the depleted aquifers.
Hence, the need for implementation of measures to ensure that
rain falling over a region is tapped as fully as possible through
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5. To conserve & augment the storage
of ground water
To reduce water table depletion
To improve the quality of ground
water
 To arrest sea water intrusion in
coastal areas
To avoid flood & water stagnation in
urban areas
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6.  It is the activity of direct collection of rain water
 Rain water can be stored for direct use or can be
recharged into the ground water aquifer
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7.  groundwater is scarce
 groundwater is contaminated
 terrain is rugged or mountainous
 seismic & flooding events are common
 the aquifer is at risk of saltwater intrusion
 population density is low
 electricity & water prices are rising
 water is too hard or mineral laden
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8. HOW TO HARVEST RAINWATER
Broadly there are two ways of
harvesting rainwater
(i) Surface runoff
harvesting
(ii) Roof top
rainwater
harvesting
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9.  – Broadly there are two ways of harvesting
rainwater
 Surface runoff harvesting
 Roof top rainwater harvesting
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10.  .
 In urban area rainwater flows away as
surface runoff. This runoff could be caught
and used for recharging aquifers by adopting
appropriate methods
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11.  It is a system of catching rainwater where it
falls. In rooftop harvesting, the roof becomes
the catchments, and the rainwater is
collected from the roof of the
house/building. It can either be stored in a
tank or diverted to artificial recharge
system. This method is less expensive and
very effective and if implemented properly
helps in augmenting the ground water level
of the area.
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2. Roof catchment systems
System components
Domestic rainwater harvesting system
consist of:
• a collection surface,
• a storage tank, and
• guttering or channels to transport the
water from one to the other.
Peripheral equipment sometimes
incorporated:
• a first-flush system,
• a filtration equipment, and
• settling chambers

13. TYPES OF FILTERS USED FOR RAIN WATER
HARVESTING
1. Sand Gravel Filter
These are commonly used filters, constructed by brick
masonry and filleted by pebbles, gravel, and sand as
shown in the figure. Each layer should be separated by
wire mesh.
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14. 2. Charcoal Filter
Charcoal filter can be
Made in-situ or in a
drum. Pebbles, gravel,
sand and charcoal as
shown in the figure
should fill the drum or chamber. Each layer
should be separated by wire mesh. Thin
layer of charcoal is used to absorb odor if
any.
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15. 3. PVC- Pipe filter
This filter can be made by PVC pipe of 1 to 1.20 m
length; Diameter of pipe depends on the area of roof. Six
inches dia. pipe is enough for a 1500 Sq. Ft. roof
and 8 inches dia. pipe should be used
for roofs more then 1500 Sq. Ft. Pipe
is divided into three compartments
by wire mesh. Each component
should be filled with gravel and
sand alternatively as shown in the
figure. A layer of charcoal could also be inserted
between two layers. Both ends of filter should have
reduce of required size to connect inlet and outlet. This
filter could be placed horizontally or vertically in the
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3. Ground & rock catchment systems
Large (top) and small (left) ground and rock catchment (bottom right)
Source: MBUGUA unknown; http://www.irc.nl/redir/content/download/128508/350879/file/TP40_7%20Rain%20water%20harvesting.pdf [Accessed 1.6.2010]
System components
Ground & rock catchment systems consist
of:
• a collection surface,
• a storage tank, and
• guttering or channels

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Gully plugs and nala bunds help to control the flow of water, sedimentation and recharge ground water
aquifers
Gully plugs and nala bunds
4. Watershed management

19. • Tankas
Tankas (small tank) are underground tanks, found traditionally in
most Bikaner houses.
• Khadin
A khadin, also called a dhora, is an ingenious construction designed
to harvest surface runoff water for agriculture. Its main feature is a
very long (100-300 m).
• Vav / vavdi / Baoli / Bavadi
Traditional stepwells are called vav or vavadi in Gujarat, or baolis or
bavadis in Rajasthan and northern India
• Ahar Pynes
This traditional floodwater harvesting system is indigenous to south
Bihar.
• Zings
Zings are water harvesting structures found in Ladakh. They are
small tanks, in which collects melted glacier water.
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20.  Total annual rainfall in India: 400 million
hectare-meters (area x height)
 India’s area: 329 million hectares
 If evenly spread, average height: 1.28m
 Actual distribution:
 Highly skewed area-wise
 Thar desert receives less than 200mm annually,
while Cherrapunji receives 11,400mm
 But almost every part of India receives at least
100mm annually
 Key: even 100mm annual rainfall
sufficient if harvested properly and
where it falls
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 Tankas (small tank) are underground tanks, found traditionally in most Bikaner
houses.
 Built in the main house or in the courtyard.
 Circular holes made in the ground, lined with fine polished lime, in which raiwater
was collected.
 Tankas were often beautifully decorated with tiles, which helped to keep the water
cool. The water was used only for drinking.
 If in any year there was less than normal rainfall and the tankas did not get filled,
water from nearby wells and tanks would be obtained to fill the household tankas.
 The tanka system is also to be found in the pilgrim town of Dwarka where it has
been in existence for centuries. It continues to be used in residential areas,
temples, dharamshalas and hotels.

22.  Practiced in Jaisalmer area
 Not enough rain to fulfill crop
requirements
 Designed to harvest surface runoff
water for agriculture.
 Its main feature is a very long
(100-300 m) earthen embankment
(khadin bund) built across the
lower hill slopes lying below
gravelly uplands.
 Sluices and spillways allow excess
water to drain off.
 The khadin system is based on the
principle of harvesting rainwater
on farmland and subsequent use
of this water-saturated land for
crop production.
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23.  10-12 m deep pits dug near tanks to collect
the seepage. Kuis can also be used to
harvest rainwater in areas with meagre
rainfall.
 The mouth of the pit is usually made very
narrow. This prevents the collected water
from evaporating.
 The pit gets wider as it burrows under the
ground, so that water can seep in into a
large surface area.
 The openings of these entirely kuchcha
(earthen) structures are generally covered
with planks of wood, or put under lock and
key.
 The water is used sparingly, as a last
resource in crisis situations.
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24.  Nadis
 Natural surface depression which receives rain
water from different directions
 They receive their water supply from erratic,
torrential rainfall.
 Can lead to heavy sedimentation and siltation
 Trees can prevent some of this
 Dredging out the sediment before monsoon can also
help
 Can lose water by evaporation
 Talabs, lakes are similar
 Toba is similar as well – natural depression
with a natural catchment area
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25.  Traditional stepwells are called vav or vavadi in Gujarat,
or baoris or bavadis in Rajasthan and northern India.
 They were secular structures from which everyone could
draw water.
 Most of them are defunct today.
 Stepwell locations often suggested the way in which they
would be used.
 Within or at the edge of a village - utilitarian purposes and as a
cool place for social gatherings.
 Outside the village, on trade routes - resting places.
 When stepwells were used exclusively for irrigation, a
sluice was constructed at the rim to receive the lifted
water and lead it to a trough or pond, from where it ran
through a drainage system and was channeled into the
fields.
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27.  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.
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31. Catchment Area
• Rooftop
• Land surface
Collection Device
• Storage tanks
• Rain barrel
• Water cistern
Conveyance System
• Gutters
• Down-pipes
• Pumps
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32. Slow it, Spread it,
Sink it!
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 Catchment Area/Roof
- the surface upon which the rain falls
 Gutters and Downpipes
- the transport channels from catchment surface to
storage
 Leaf Screens and Roofwashers
- the systems that remove contaminants and debris
 Cisterns or Storage Tanks
- where collected rainwater is stored
 Conveying
- the delivery system for the treated rainwater, either by
gravity or pump
 Water Treatment
- filters and equipment, and additives to settle, filter, and
disinfect
RWH System Components

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 Rainfall quantity (mm/year)
 Rainfall pattern
 Collection surface area (m2)
 Runoff coefficient of collection (-)
 Storage capacity (m3)
 Daily consumption rate (litres/capita /day)
 Number of users
 Cost
 Alternative water sources
Factors affecting RWH system design

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 Catchment Area/Roof
- the surface upon which the rain falls
 Gutters and Downpipes
- the transport channels from catchment surface to
storage
 Leaf Screens and Roofwashers
- the systems that remove contaminants and debris
 Cisterns or Storage Tanks
- where collected rainwater is stored
 Conveying
- the delivery system for the treated rainwater, either by
gravity or pump
 Water Treatment
- filters and equipment, and additives to settle, filter, and
disinfect
RWH System Components

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39. Diameter Of pipe
(mm)
Average rate of rainfall in mm/h
50 75 100 125 150 200
50 13.4 8.9 6.6 5.3 4.4 3.3
65 24.1 16.0 12.0 9.6 8.0 6.0
75 40.8 27.0 20.4 16.3 13.6 10.2
100 85.4 57.0 42.7 34.2 28.5 21.3
125 - - 80.5 64.3 53.5 40.0
150 - - - - 83.6 62.7
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40. DO'S AND DON’TS
Harvested rainwater is used for direct usage or for
recharging aquifers. It is most important to ensure that
the rainwater caught is free from pollutants. Following
precautionary measures should be taken while
harvesting rainwater:-
Roof or terraces uses for harvesting should be clean, free from
dust, algal plants etc.
Roof should not be painted since most paints contain toxic
substances and may peel off.
Do not store chemicals, rusting iron, manure or detergent on the
roof.
Nesting of birds on the roof should be prevented.
Terraces should not be used for toilets either by human beings or
by pets.
Provide gratings at mouth of each drainpipe on terraces to trap23-09-2016Training Module for MBSE AMBAJOGAI COE 40

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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 :
1991
6. Indian Railway Works Manual 2000
7. www.rainwaterharvesting.org
8. www.aboutrainwaterharvesting.com

43. Happy rainwater
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