Prayas Session: Rain Water Harvesting by Soumalya Nandi

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Tenet Systems Pvt. Ltd.An ISO 9001:2008 Certified Company

Wednesday Work-out session – 21th May 2014

Presented By – Soumalya Nandy

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o A technique used to collect, store, and use rainwater for efficient application and conservation

o An effective way of utilizing large amount of water which otherwise goes as surface runoff.

Traditionally, rainwater harvesting has been practiced in arid and semi-arid areas, and has provided drinking water, domestic water, water for small irrigation and a way to replenish ground water level.



o Industrialization and Urbanization(a) Increase in per capita utilization(b) Less peculation area

o In places where rain fed/ irrigation based crops are cultivated through ground watero Decrease in surface area of Lakes, Pondso Changing of climateso Deforestation(i) Less precipitation(ii) Absence of Barriers

(a) Rain drops checked by leaves of tree(b) Water slowly descends through twigs & trunk(c) Humus – acts as reservoir

1 hectare of forest-6-7 Lac ton of water

(after filtering) top layer can hold 1.2 Lac tons of water


We have to find an efficient resource for continuous supply of water. Water should be purified( non polluted ) so to use it in drinking, domestic or any other purpose. Quantity of water should meet the basic requirements specially for rural areas.

Rain water• is the ultimate source of fresh water.• has potential to meet water demand is tremendous.• harvesting helps to overcome water scarcity.• help to conserve aquifers by recharging it with water

Rain water harvesting is the ultimate answer!


Broadly rainwater can be harvested for two purposes:

•Storing rainwater for ready use in containers above or below ground•Charged into the soil for withdrawal later (groundwater recharging)


This is perhaps one of the most frequently asked question, as to why one should harvest rainwater. Some of the reasons are following

o Improvement in• ground water levels• water availability in wells/tube-wells• quality of ground water through dilution• living condition in rural areas

o Reduction in soil erosion due to reduced surface water runoffo Conservation of surface water runoff during monsoono Outdoor(ex. Watering plants or car wash etc.) or domestic(bathing animals etc.) purpose useo Inculcate a culture of water conservation


o RWH - yield copious amounts of water. For an average rainfall of 1,000mm, approximately four million litters of rainwater can be collected in a year in an acre of land (4,047 m2), post-evaporation.

o As RWH - neither energy-intensive nor labour-intensive

o It can be a cost-effective alternative to other water-accruing methods.

o With the water table falling rapidly, & concrete surfaces and landfill dumps taking the place of water bodies, RWH is the most reliable solution for augmenting groundwater level to attain self-sufficiency


“Catch rain where it falls.”- Rainwater harvesting can be harvested from the following surfaces:

• Rooftop : If buildings with impervious roofs are already in place, the catchment area is effectively available for free of charge.- Roof rain water harvesting.

• Paved and unpaved areas : i.e. open fields, parks, roads and pavement and other open areas can be effectively used to harvest the runoff. The main advantage is that water can be collected from a larger area. – Land based rain water harvesting.

• Water bodies : The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirement of the city, it also recharges ground water aquifers. – Water shed harvesting.


There are two main techniques of rain water harvestings.• Storage of rainwater on surface for future use.• Recharge to ground water.

The storage of rain water on surface is a traditional techniques and structures used were roof top harvesting , underground tanks, ponds, check dams, weirs etc.

In case of ground water pits, trenches, dug well, shaft etc.


The illustrative design of the basic components of roof top rainwater harvesting system is given in the following typical schematic diagram/

The system mainly constitutes of following sub components:o Catchmento Transportationo First flusho Filtero Store

Catchment : The surface that receives rainfall directly is the catchment of rainwater harvesting system. It may be terrace, courtyard, or paved or unpaved open ground. The terrace may be flat /stone roof or sloping roof. Therefore the catchment is the area, which actually contributes rainwater to the harvesting system.


Transportation : It is a process by which rain water flow from roof to the purification system and then finally to the storage tank by the help of pipes and valves.

First flush : This is a process of rain water pre filter. Rainwater captured from rooftops contains significant quantities of plant debris, soil, eroded roof materials, and other solids that can clog pumps, valves, and pipes. Very small solid substance collect as sediment at the bottom of storage tanks, reducing tank storage capacity. Organic solids remain in suspension and decompose, depleting oxygen and generating hydrogen sulfide and other noxious by-products. To improve the quality of rainwater we have to install a “roof washer” or “first-flush diverter”, a device that discards the initial runoff from a roof before it reaches the storage tank.


A First-Flush Diverter retains the initial runoff from a roof in a length of pipe that is capped at the end. When the pipe is filled, a ball or flapper shuts off the top of the pipe so that additional rainfall flows directly into the rainwater storage tank. The pipe cap has a small-diameter outlet that slowly releases the “first-flush” water so that by the next rain the pipe is empty and is ready to receive more water. There are three standard sizes that utilize 3”, 4”, and 12” pipe for water storage.


Filter : After fill the first flush diverter water comes into filter chamber which containing with different purification materials like sand, small brick, charcoal, pebble etc places in separate permeable layer. Water get purified by going through different layers. Then finally to storage.


Store : After get purified water store in tanks for future use.


o In term of complex constructions or use best quality of materials there is a requirement for high cost.o Repairing parts or maintenance will add cost or expenditure for specific period of time.o If not maintain properly then it can cause various problems in term of transport of water to storage.o If the storage tank did not washed properly with in a period then it will decrease the quality of water.



Check dams/Nala plugging : It is 1.5 to 2 meters height constructed across streams with gentle slopes. It consist with impermeable substances. It will force to change the direction of stream to travel water in different areas for conservation.


Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :-

Pits : Recharge pits are constructed for recharging the shallowaquifer. These are constructed 1 to 2 m, wide and to 3 m. deepwhich are back filled with boulders, gravels, coarse sand.

Trenches : These are constructed when the permeable stream isavailable at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to1.5m. deep and 10 to 20 m. long depending up availability of water.These are back filled with filter materials.



Dug wells : Existing dug wells may be utilized as recharge structure and watershould pass through filter media to remove silts before putting into dug well.Periodic chlorination required.


Spreading techniques : When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.

Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and back filled with boulders, gravels & coarse sand.

Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarse sand.


Some of them are following : o It is less expensive and economic resourceo It is sustainable and reliable source of water supplyo It is relatively less vulnerable to pollutiono Needs little treatment before use.o It has no turbidity and colouro There is no conveyance losses in ground water based supplies.o It is key to life in arid and semi-arid regions.o It is usually universally availableo There is more ground water than surface water


A noble goal – A common responsibility

Ground water exploitation is inevitable In Urban areas. But the ground water potential is getting reduced due to urbanization resulting in over exploitation. Hence, a strategy to implement the ground water recharge, in a major way need to be launched with concerted efforts by various Governmental and Non-Governmental Agencies and Public at large to build up the water table and make the ground water resource, a reliable and sustainable source for supplementing water supply needs of the urban dwellers.

Recharge of ground water through storm run off and roof top water collection, diversion and collection of run off into dry tanks, play grounds, parks and other vacant places are to be implemented by Special Village Panchayats/ Municipalities /Municipal Corporations and other Government Establishments with special efforts.



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Call: +919830158077 or

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Web: http://tenetsystems.net

Environment

Prayas Session: Rain Water Harvesting by Soumalya Nandi