Rainwater harvesting

1. Rainwater harvesting

2. What is rain water harvesting
•The collection and storage of rain water
for
later productive use is defined as
rainwater harvesting

3. How?
Recharge if there’s excess
The concept is simple
Collect
Store
Use

4. Components of roof top
rainwater harvesting
Any rainwater harvesting system has three
components
• Catchment
•Conveyance
•Filters
•Storage

5. ROOFTOP RAINWATER HARVESTING
Catchment – rooftop
Transportation – Down take pipes
Filters – First flush device
Leaf and grit filter
Storage – Tank / well
Components

7. Catchment
•Rooftops are favoured because of the
large coefficient of run-off generated from
them and relatively less likelihood of their
contamination.
• Conveyance
•rooftops rainwater gutters and rainwater
down pipes are conveyance systems

8. Storage
•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.

9. Catchment

10. The water that leaves the rooftop may be 65 – 90% of
the water that falls on it
Roof material absorbs some water
More water loss if roof is flat
Evaporation losses

11. Keep the roof clean
•Remove leaves, plant debris,
bird and animal droppings, dead
rodents or birds
•No tar / bitumen on the roof
•No chemical pesticides or
fertilizers for rooftop garden

12. Conveyance

13. How much water can we harvest?
Rain Water Collected
From Both Sides of the
Roof
W
Rain Water
Collected From one
Side of the Roof
Amount of rainfall
(mm)
x =
W
Catchment Area
(m2)
Volume of water received
(Litres)

14. Transportation
Pipe size is calculated based on peak flow rates
(rooftop area and peak rainfall rate)
Gutter (open on top)
Downtake pipe (cylindrical)
PVC pipes preferred. Do not use lead pipes

15. Take care….
•Clamp gutters and down take pipes well
•Keep gutters clean of leaves
•See that leaves do not clog a down take pipe
(Jaali or leaf filter may be needed at rooftop discharge point
but this may also be a problem if leaf debris collects on it
and water stagnates on the roof)
•Gutters and down take pipes should be gently sloping
towards the storage tank, so that there is no stagnation of
water in the pipe

16. Filters

17. Filters
Gravel
Sand
Inlet
Out flow
Over flow
Gravel
Recharge tank
Filter
Storage tank
Down take pipes
First flush
Check and clean filters before and after each rainy season
Make your own filter with sand,
charcoal and gravel
Or
Buy a filter off the shelf

18. 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
regularly.
First flush standpipe

21. Storage

22. 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

23. • 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.
Storage tank features

24. 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

25. Other factors
•Some changes may be required in
plumbing, if retrofit
•Clean rwh system regularly
–Rooftop everyday
–Tank after a rainy season
–Filter after a rainy season

26. Rainwater
Harvesting
DO
IT
NOW!

27. Why?
At the city level
●
Reduces water demand

●
Reduces energy demand – lesser energy required for water distribution

●
Improves groundwater situation

●
In coastal areas, it can counter saline water intrusion into freshwater aquifers

●
Prevents urban flooding

28. Why?
At the school level

• Reduces water bills

• Sets an example for students and parents

• Improves groundwater table if rainwater is recharged

• Improves groundwater quality by dilution
(rainwater has nearly neutral pH and zero hardness)

29. ROOFTOP RAINWATER HARVESTING
Catchment – rooftop
Transportation – Down take pipes
Filters – First flush device
Leaf and grit filter
Storage – Tank / well
Components

30. How much water can we harvest?
Rain Water Collected
From Both Sides of the
Roof
W
Rain Water
Collected From one
Side of the Roof
Amount of rainfall
(mm)
x =
W
Catchment Area
(m2)
Volume of water received
(Litres)

31. Transportation
Pipe size is calculated based on peak flow rates
(rooftop area and peak rainfall rate)
Gutter (open on top)
Downtake pipe (cylindrical)
PVC pipes preferred. Do not use lead pipes

32. Take care….
•Clamp gutters and down take pipes well
•Keep gutters clean of leaves
•See that leaves do not clog a down take pipe
(Jaali or leaf filter may be needed at rooftop discharge point
but this may also be a problem if leaf debris collects on it
and water stagnates on the roof)
•Gutters and down take pipes should be gently sloping
towards the storage tank, so that there is no stagnation of
water in the pipe

33. Filters
http://www.rainyfilters.com/rainwater.aspx
Gravel
Sand
Inlet
Out flow
Over flow
Gravel
Recharge tank
Filter
Storage tank
Down take pipes
First flush
Check and clean filters before and after each rainy season
Make your own filter with sand,
charcoal and gravel
Or
Buy a filter off the shelf

34. 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
regularly.
First flush standpipe

35. STORAGE SIZE

Depends on
•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
Do a water
audit to check
water
requirement.

36. STORAGE
•Above ground
–Ground level or Intermediate floor level
–Just below roof
•Below ground
Save on pumping cost

37. 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

38. • 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.
Storage tank features

39. 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

40. Other factors
•Some changes may be required in
plumbing, if retrofit
•Clean rwh system regularly
–Rooftop everyday
–Tank after a rainy season
–Filter after a rainy season

41. Rainwater
Harvesting
DO
IT
NOW!

42. Rooftop
Rainwater
Harvesting
Pre-implementation
guide for schools