Components

A Roof water harvesting system should have the following components:

Down pipe and first flush arrangement

This is an arrangement to prevent the dust and other unwanted materials that may be seen on the roof, from reaching the storage tank. By fitting a down pipe with an end cap or valve can ensure that the washed water from the roof does not reach the storage tank. It is always safe to ensure that the first flush arrangement remains open during non- rainy days and should be closed after first rain up to the satisfaction of the end user.

Filter unit

The rainwater collected from the roof should be allowed to reach the storage tank only through a filtering mechanism. Rubble, sand and charcoal, as used in the traditional three-pot filtration, can be adopted here. 10 cm thick 20mm rubbles, 10 cm thick charcoal/coconut shell, 15 cm thick coarse sand, 5 cm thick 6mm rubbles etc. may be arranged from bottom to top in the filter unit. The water that is passed through this filter should remain safe for a long period of storage. Charcoal/coconut shell is added to eliminate gaseous pollutants.

Storage tank

Mainly three types of storage tanks are constructed for roof water harvesting. They are aboveground, underground or sub surface tanks.

Provision for drawing water and spill over

For drawing water from the storage tanks any method may be adopted provided it shall be drawn only when needed. The easier the method adopted for drawing water, the more will be the chances for its misuse. Three types of drawing water are usually adopted. They are by using a tap (small capacity tanks with basement and over ground tanks), hand pump (under ground tanks) or electric pump sets (large capacity tanks).