The benefits of owning and using a cistern are considerable. Cisterns reduce the need for treated municipal water for uses such as landscaping, toilet flushing, and laundry. They also reduce peak storm water volume, which is a main concern in certain areas. Rain barrels and cisterns can reduce runoff volume and, for smaller storm events, delay and reduce peak runoff flow rates. By storing and diverting runoff from impervious areas such as roofs, these devices reduce the undesirable impacts of runoff that would otherwise flow directly and quickly into receiving waters and contribute to flooding and erosion.
Cisterns are commonly used as a secondary source of water for gardening and other tasks in residential areas. In these areas, larger sized cisterns can be adapted to supplement potable water supplies. Many water districts and city governments encourage the use of cisterns for potable water as they can provide a source of chemically untreated water, free of most sediment and dissolved salts. Residential irrigation can account for up to 40% of domestic water consumption and can therefore be very expensive. The use of cisterns and rain barrels can reduce these costs considerably.