Rainwater harvesting techniques

1. WATER HARVESTING IN
CITIES AND ITS
SUSTAINABILITY
AGR 202 – WATER MANAGEMENT(1+1)

2. WATER HARVESTING
 It means capturing rain where it falls or capturing the run
off in your own village or town. And taking measures to
keep that water clean by not allowing polluting activities.
 In general, water harvesting is the activity of direct
collection of rainwater. The rainwater collected can be
stored for direct use or can be recharged into the
groundwater.

3. METHODS OF WATER HARVESTING
water harvesting can be undertaken through a variety
of ways :
 Capturing runoff from rooftops
 Capturing runoff from local catchments
 Capturing seasonal floodwaters from local streams
 Conserving water through watershed management
Water harvesting potential = Rainfall (mm) x Collection efficiency

5. Groundwater
 India has the single largest exploitation of
groundwater in the world with over 20 million
bore-wells
 65 % of the net irrigated land gets water from
bore-wells
 85 % of urban habitations depend on groundwater

6. How much water do I use ?
Use Litres/person
Drinking 3
Cooking 4
Bathing 20
Flushing 40
Washing-
clothes
25
Washing
Utensils
20
Gardening 23
TOTAL 135
Consumption range :
from 50 to 300 liters per person per day

8. In the year 2001, Chennai finally decided to tackle the
problem of water scarcity.
Rainwater harvesting was made compulsory for all
houses in the city.
And today, Chennai is home to over 5,00,000 rainwater
harvesting systems, highest for any city in the world.
 Bangalore is not too far behind with rainwater
harvesting being made compulsory in the city.
Moreover, the state government also provides guidance
and training on methods of rainwater harvesting.
Even Kerala houses some 4.5 million open wells, the
largest density of open wells for any place in the world.
STATUS OF RWH IN CITIES

9. Rainwater harvesting in Bangalore city
 At the city level rainwater is collected in many
lakes and allowed to infiltrate and recharge the
groundwater
 At individual buildings, rainwater is harvested
either by storing in sump tanks or by recharging
through small wells.
 Rainwater harvesting has been implemented in
23,683 schools in Karnataka State

10. Outlook of Rainwater harvesting
 Collecting and storing rainwater for future
productive use. Storing can also be in aquifers
through artificial recharge systems
 Mimicry Hyrological cycle.
 A rainwater harvesting system consists of
catchment , conveyance, filtration and storage or
recharge structure.

11. Rainwater harvesting systems
installed in Multistoried buildings
can suffice for daily water usage
by the building residents :
 Rainwater collected in the roof
flows down the pipes running
down the length of building, into
Service Wells or Percolation Pits
 Water trickles down the layer of
Pebbles and Boulders designed
for underground filtration
 Filtered water flows into either
Recharge Well or the Collection
Chambers
 With this setup, the building can
draw water readily from its
water table in the basement,
without any shortage in supply

12. Hydro-flows from a small plot
Before building After building
Surface runoff 15 % 90%
Recharge 10 % 5%
Evapo-transpiration 75 % 5%
 The aim of rainwater harvesting is bio-mimicry. To restore
the local hydrology on a plot as before building.

13. DIAGRAMMATIC VIEW OF RWH

14. A TYPICAL RAINWATER HARVESTING SYSTEM
WITH FILTER & SUMP FOR A RESIDENCE

15. •In
containers
Collect
•Filters
Store
•Household
•Gardening
Use
PURPOSE

16. ROOF TOP RAINWATER HARVESTING
 Rooftop Rain Water Harvesting is the technique through which
rain water is captured from the roof catchments and stored in
reservoirs.
 Rooftop rainwater harvesting systems are now mandatory for
new buildings in 18 of India’s 28 states and four of its seven
federally-administered union territories, according to India’s
Press Information.
 The Main Objective of rooftop rain water harvesting is to make
water available for future use. Capturing and storing rain water
for use is particularly important in dryland, hilly, urban and
coastal areas.

17. 1. Rain water collected from the roof is
channelized through the pipe that drains
it into the De-siltation Tanks.
2. The water accumulated, seeps into the
Ferro-Cement Tank from the De-siltation
Tanks.
3. Percolation Pits are one of the easiest
and most effective means of harvesting
rainwater, measuring not more than
60 x 60 x 60 cm. They are usually filled with
pebbles or brick jelly and river sand,
covered with perforated concrete slabs.
4. Water can be withdrawn via outlets like
tap attached to the De-siltation tanks or
Tube Wells pumping out fresh water from
the Ferro-Cement Tanks.

18. PICTORIAL VIEW OF RTRWH

19. Roof Water Harvesting …….. a quick summary
 Rooftop Rain Water Harvesting – Capturing of rain from roof catchments
and storing it in containers or sub-surfacee
ground water reservoirs.
 ADVANTAGES:
1. Reduced ‘ground-water pumping’ cost
2. High quality water, low in mineral content
3. Reduced soil erosion rates in urban areas
4. Less expensive and easy to construct, operate & maintain
 PRECAUTIONS:
1. Filters should be provided to avoid silting of
hand-pumps and tube-wells.
2. Storage tanks should not be close to sources of
contamination (eg. Septic tank)
3. Setup should be regularly cleaned & disinfected
4. Speed breaker plate should be provided below inlet
pipe so as to not disturb the filter material.

20. METHODS OF RTRWH
Roof top rain water/storm runoff harvesting through
 Recharge Pit.
 Recharge Trench.
 Tubewell.
 Trench with Recharge Well.

21. 1.Roof Top Rainwater Harvesting through
Recharge Pit:

22. 2.Roof Top Rain Water Harvesting through
Recharge Trench:

23. 3.Roof Top Rain Water Harvesting through
Existing Tubewells

24. INTERESTING FACTS
The New Delhi-based Centre for Science and
Environment estimates that merely capturing the rain
water and run off on 2 per cent of India’s land area could
supply 26 gallons of water per person.(1 gallon = 3.76
litres)

25. SUPPORTING SYSTEM
 About 50 percent of the funds for India’s rural
employment act are being used for water harvesting
systems, said the Minister for Rural Development.
 National Water Harvesters Network (NWHN)
 In Delhi 50% subsidy for RWH.

27. A simple traditional rainwater harvesting system

28. Formula:
Total quantity of water to be collected (cu.m.) =
Roof Top Area (Sq.m.) x Average Monsoon Rainfall (m) x 0.8
For Example :
IN CHENNAI , Average Monsoon Rainfall = 1218.6 mm.(1.2186 m)
Roof top area = 50 sq.m (small house)
Total quantity of water to be collected = 60.93 cu.m
i.e (60930 litres)
Water requirement for per head per day in urban = approx.100 lit
water requirement for per head per year in urban = 36500 litres
cost of establishment : 2,00,000. In Delhi 50% subsidy for RWH
NOTE : 0.8 represents collection efficiency of rainfall

29. USES
 Provide drinking water
 Provide irrigation water
 Increase groundwater recharge
 Reduce stormwater discharges, urban floods and
overloading of sewage treatment plants
 Reduce seawater ingress in coastal areas.

30. EVERY ROOF IN A CITY CAN BE A CATCHMENT

31. Rainwater harvesting in an underground tank

32. A first rain separator and a sand filter

33. Harvested rainwater in underground tank

34. Back-filling. Round hard stones Smaller stones on top
Filling of the recharge pit with large stones first
than small stones.

35. Finished recharge pit with coarse sand
filling over the small stones

36. Recharge pit around bore wells

37. The pit has reach the silt layer
Pit and concrete rings
Placing of the rings
The making of a recharge well – to put rooftop rainwater or stormwater into the aquifer.
In Bangalore city, typically 6 metres deep and 1 metre diameter.

38. LANDSCAPED GARDENS

39. Rainwater going inside a recharge well
Re-charging a bore well Outlet pipe in recharge well

40. Don’t forget the maintenance

41. Recharge wells in storm-water drains

42. Conclusion :
Most metro cities in India are water starved but not rain starved. We should not
forget the fact that water harvested is water produced and make sincere attempts
to harvest every drop of water that falls within every premises, locality, city and
country before thinking in terms of mega projects like interlinking of rivers,
desalination of sea water etc

44. Our Civilization Needs Water To Sustain
Let Us Save It Together !!