Cisterns are essentially large tanks used to collect rainwater that would otherwise run off into the ground from rooftops or other catchment areas. Cisterns can be located both above or below ground level, and come in a variety of styles, from nondescript plastic containers, to ornate decorative pieces. During significant rainfall events, the water channeled from gutters on the roof into a large cistern will serve multiple residential uses. An average roof can collect 400 gallons of water in a ½ inch rainfall event. This water can then be used for irrigation, the flushing of toilets, and even for drinking water once properly filtered. Well-filtered and treated rainwater can even be cleaner than water provided by the city.
Cisterns provide a dual service by also preventing the roof runoff from entering the stormwater system in a large rainfall event. Doing so incorporates one of the central goals of sustainability: to reduce one’s footprint on the surrounding area. By containing a large portion of a property’s rainfall, all of that excess will now stay on site and prevent the whole system from being overloaded.