Stormwater harvesting or stormwater reuse is the collection, accumulation, treatment or purification, and storage of stormwater for its eventual reuse. While rainwater harvesting collects precipitation primarily from rooftops, stormwater harvesting deals with collection of runoff from creeks, gullies, ephemeral streams, and other ground conveyances. It can also include catchment areas from developed surfaces, such as roads or parking lots, or other urban environments such as parks, gardens and playing fields.
Water that comes into contact with impervious surfaces, or saturated surfaces incapable of absorbing more water, is termed surface runoff. As the surface runoff travels greater distance over impervious surfaces it often becomes contaminated and collects an increasing amount of pollutants. A main challenge of stormwater harvesting is the removal of pollutants in order to make this water available for reuse.
Stormwater harvesting projects often have multiple objectives, such as reducing contaminated runoff to sensitive waters, promoting groundwater recharge, and non-potable applications such as toilet flushing and irrigation. Stormwater harvesting is also practiced in areas of the United States as a way to address rising water demands as population rises. Internationally, Australia is notable in its active pursuit of stormwater harvesting.