rainwater harvesting
TRANSCRIPT
Rainwater harvesting
What is rain water harvesting
• The collection and storage of rain water for
later productive use is defined as rainwater harvesting
How?
Recharge if there’s excess
The concept is simple
Collect
Store
Use
Components of roof top rainwater harvesting
Any rainwater harvesting system has three components
• Catchment
• Conveyance
• Filters
• Storage
ROOFTOP RAINWATER HARVESTING
Catchment – rooftop
Transportation – Down take pipes
Filters – First flush device
Leaf and grit filter
Storage – Tank / well
Components
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
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.
Catchment
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
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
Conveyance
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)
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
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
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
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
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
• 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
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!
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)
ROOFTOP RAINWATER HARVESTING
Catchment – rooftop
Transportation – Down take pipes
Filters – First flush device
Leaf and grit filter
Storage – Tank / well
Components
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)
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
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
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
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
Excess water can be diverted into a groundwater recharge system
Do a water audit to check water requirement.
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
• 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
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!
Rooftop Rainwater Harvesting
Pre-implementation
guide for schools