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

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)

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

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 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!