2. Rain Water Harvesting?.
• Rain Water Harvesting RWH- process of collecting, conveying & storing
water from rainfall in an area – for beneficial use.
• Storage – in tanks, reservoirs, underground storage- groundwater
• Hydrological Cycle
3. How?
1.Collect
2.Use
3.Store
4.Recharge if there’s
excess
4. What can we use the rain water for?
If used for drinking, it is absolutely necessary to
check water quality in a lab and treat as required
5. RWH – Methodologies
• Roof Rain Water Harvesting
• Land based Rain Water Harvesting
• Watershed based Rain Water harvesting
• For Urban & Industrial Environment –
• Roof & Land based RWH
• Public, Private, Office & Industrial buildings
• Pavements, Lawns, Gardens & other open
spaces
6. Rain Water Harvesting–
Advantages
1.Provides self-sufficiency to water supply
2.Reduces the cost for pumping of ground water
3.Provides high quality water, soft and low in minerals
4.Improves the quality of ground water through dilution
when recharged
5.Reduces soil erosion & flooding in urban areas
6.The rooftop rain water harvesting is less expensive &
easy to construct, operate and maintain
7. In desert, RWH only relief
8. In saline or coastal areas & Islands, rain water
provides good quality water
7.
8. WHY Rainwater Harvesting?
•To arrest ground water decline and augment ground
water table.
•To beneficiate water quality in aquifers.
•To conserve surface water runoff during monsoon.
•To reduce soil erosion.
•To inculcate a culture of water conservation.
9. Broadly there are two ways of harvesting rainwater:
(i) Surface runoff harvesting :- In urban area
rainwater flows away as surface runoff. This runoff could
be caught and used for recharging aquifers by adopting
appropriate methods.
(ii) Roof top rainwater harvesting:- 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
12. Rooftops are favoured because
of the large coefficient of run-off
generated from them and
relatively less likelihood of their
contamination.
13. The water that leaves the rooftop may be 65 – 90% of
the water that falls on it
Roof material absorbs some water
Evaporation losses
More water loss if roof is flat
14. lead the water from the catchment
surface to the storage tank
15. FILTER AND FIRST FLUSH
DEVICES
remove grit, leaves and dirt that the
rainwater may transport from the
catchment, before the water enters the
storage tank. When it rains after a long
gap, the rooftops are usually very dirty
and the rainwater also carries with it a lot
of dissolved air pollutants. A first flush
device diverts the water from the first rain
so that it does not enter the storage tank.
16. Down take pipes
Over flow Filters
Inlet Gravel
Sand Make your own filter with
Out flow
Storage tank Gravel sand, charcoal and gravel
Or
First flush
Filter
Recharge tank Buy a filter off the shelf
Check and clean filters before and after each rainy season
17. First flush
• The first rain carries with it a lot of
filth from the rooftop and dissolved
air pollutants
• This rainwater should be diverted
away from the storage tank using a
first flush device.
• Some filters have a first flush system
integrated in them
• Check and clean first flush devices First flush standpipe
regularly.
18. DELIVERY SYSTEM
Piping systems that convey the stored
rainwater till the point of end-use.
It is not recommended to use harvested
rainwater for drinking, cooking and
dishwashing unless water quality issues are
verified and necessary treatment or
purification systems installed.
19. From the simplest ground level
tank, surface lined ponds and
large lakes storage options are
many depending on the context of
the rainwater harvesting design.
20. STORAGE
• Above ground
▫ Ground level or Intermediate floor
level
Save on pumping cost
▫ Just below roof
• Below ground
21. Storage tank features
• Durable and no leaks
• Built on a strong and stable substrate that can support the tank
filled with water
• Opaque – presence of light can cause algal growth in tank
• Secure and impervious cover
• Vents to be covered with insect proof mesh
• Located as close as possible to demand and supply points to
reduce plumbing
22. Storage tank features
• Overflow pipe should be provided close to the top, to reduce dead space.
• Overflow pipe diameter should be equal to inlet pipe diameter
• Overflow pipe should lead excess water away from the foundation of tank and other buildings.
Preferably the overflow should be led into a groundwater recharge system or a garden
• There will be sedimentation in the tank. Taps and pipes to draw water from the tank should
not be very close to the bottom to prevent sediments from entering the plumbing system
and clogging it.
23. STORAGE SIZE
Do a water
Depends on audit to
check water
requirement.
• Rainwater availability
• Water requirement
• Budget (storage tank is most expensive part of (rwh system)
• Available space and aesthetics
Excess water can be diverted into a groundwater recharge system
24. 1. Storage of Direct use
2. Recharging ground water aquifers
3. Recharging of bore wells
4. Recharge Pits
5. Soak away or Recharge Shafts
6. Recharging of dug wells
7. Recharge Trenches
8. Percolation tanks
