Rainwater harvesting involves the collection and storage of rainwater utilizing a rainwater harvesting system. In most cases, rainwater is collected from roofs or other exposed surfaces and then directed to a storage tank, groundwater well, or aquifer for subsequent use.

Stormwater harvesting is similar but not the same as rainwater harvesting. Stormwater harvesting involves the collection and storage of stormwater, generally from creeks, streams, roads, parking lots, parks, golf courses, and similar sources.

In both cases, the rainwater can be used for irrigation, recharging aquifers and grounder wells, providing water for livestock, ponds, and if treated, for domestic consumption.

Many cities and communities in California are considering laws that will make it mandatory for all new commercial buildings to be equipped with rainwater harvesting systems.