Rainwater harvesting is the gathering, or accumulating and storing, of rainwater. Traditionally, this has been practiced in arid and semi-arid areas, and has provided drinking water, domestic water, water for livestock, water for small irrigation and a way to replenish ground water levels.
However, this is now bwcoming more common for the countyryside here in the UK and even in urban areas. It helps to provide supplemental water for the city's requirement, to increase soil moisture levels for urban greenery, to increase the ground water table through artificial recharge, to mitigate urban flooding and to improve the quality of groundwater - these are just some of the reasons why rainwater harvesting can be adopted in cities.
For the household, harvested rainwater can be used for flushing toilets and washing laundry. Indeed in hard water areas it is superior to mains water for this. It can also be used for showering or bathing. It may require treatment prior to use for drinking.
There are many types of systems to harvest rainwater. The type used depends greatly on the purpose (domestic or industrial use) and to some extent also on physical and human considerations.