Rainwater harvesting is the collection and storage of rainwater for later use, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit, aquifer, or a reservoir with percolation, so that it seeps into the ground. The harvested water can also be committed to longer-term storage or groundwater recharge. Rainwater harvesting is one of the simplest and oldest methods of self-supply of water for households, having been used in South Asia and other countries for many thousands of years.

Rainwater harvesting has benefits for both urban and rural properties. The practice of rainwater harvesting ranges from simple ideas such as a rain barrel set up underneath a gutter downspout to complex systems such as for commercial buildings or systems that supply the potable water for a house. The process of rainwater harvesting involves the collection and storage of rainwater with the help of artificially designed systems that run off naturally or man-made catchment areas like rooftops, compounds, rock surfaces, hill slopes, and artificially repaired impervious or semi-pervious land surfaces.

Rainwater harvesting can be used to meet water requirements throughout the year without the need for huge capital expenditure. It provides an independent water supply during water restrictions and can decrease a households water costs or overall usage levels. In areas where clean water is costly or difficult to come by, rainwater harvesting is a critical source of clean water. Harvested rainwater can provide a source of alternative water to federal facilities, and with additional filtration and disinfection, harvested rainwater can also be treated to potable standards to supplement municipal potable water supplies to facilities.

Rainwater harvesting is a sustainable process that helps in preserving water and is becoming a viable alternative for supplying households and businesses with water.