The collection and storage of rain, rather than allowing it to run off.
Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), aquifer or a reservoir with percolation. Dew and fog can also be collected with nets or other tools. Rainwater harvesting differs from stormwater harvesting as the runoff is collected from roofs, rather than creeks, drains, roads or any other land surfaces. Its uses include watering gardens, livestock,irrigation, domestic use with proper treatment, and domestic heating. 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, and residential and household scale projects usually financed by the user. However, larger systems for schools, hospitals and other facilities can run up costs only able to be financed by companies, organization and governmental units.