Rainwater Harvesting
Rainwater harvesting is the collection of rainwater that would otherwise have flowed into the drainage system or ground, or been lost to the atmosphere through evaporation.
Large surfaces such as roofs or driveways are ideal for rainwater harvesting. The most simple example of rainwater harvesting is a domestic garden rainwater collection butt. To maximise the amount of water collected, water butts should be fitted to a drainpipe. Pumps are available to enable the use of hoses with trigger sprays.
Another typical solution is the diversion of rainwater from the roof via a drainpipe into a storage tank (usually underground). Leaves and debris are filtered out before the water is stored. The filtered water cannot be used for drinking, but can supply toilets, outside taps, washing machines, etc. through a separate pipe network.
A control unit monitors the water level in the tank. If levels are low, the system switches to the mains water supply and if levels are high, an overflow trap allows floating material to be skimmed off and water to flow to a storm drain.
At a household level, payback periods for the more complex systems (i.e. use of rainwater to flush toilets, etc.) are long, typically more than fifteen years. However, larger projects such as schools and offices have a short payback time, often less than 5 years.