Transcript Rooftop Rainwater Harvesting Pre-implementation guide for schools Why? At the city level • Reduces water demand • Reduces energy demand – lesser energy required for water distribution •

Rooftop
Rainwater
Harvesting
Pre-implementation
guide for schools
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
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)
How?
The concept is simple
Collect
Store
Use
Recharge if there’s excess
ROOFTOP RAINWATER HARVESTING
Components
Catchment – rooftop
Transportation – Down take pipes
Filters – First flush device
Leaf and grit filter
Storage – Tank / well
How much water can we harvest?
Catchment Area
(m2)
Amount of rainfall
(mm)
x
Volume of water received
(Litres)
=
W
Rain Water
Collected From one
Side of the Roof
W
Rain Water Collected
From Both Sides of the
Roof
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
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
Transportation
Gutter (open on top)
Downtake pipe (cylindrical)
PVC pipes preferred. Do not use lead pipes
Pipe size is calculated based on peak flow rates
(rooftop area and peak rainfall rate)
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
Filters
Down take pipes
Over flow
Inlet
Gravel
Sand
Out flow
Storage tank
Make your own filter with sand,
charcoal and gravel
Gravel
Or
First flush
Filter
Recharge tank
Buy a filter off the shelf
http://www.rainyfilters.com/rainwater.aspx
Check and clean filters before and after each rainy season
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
STORAGE SIZE
Depends on
•
Rainwater availability
•
Water requirement
•
Budget (storage tank is most expensive part of (rwh system)
•
Available space and aesthetics
Do a water
audit to check
water
requirement.
Excess water can be diverted into a groundwater recharge system
STORAGE
•
•
Above ground
–
Ground level or Intermediate floor level
–
Just below roof
Below ground
Save on pumping cost
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
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.
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
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
Rainwater
Harvesting
DO
IT
NOW!