Cistern at the Chicago Center for Green Technology (Source: Abby Hall, U.S. EPA)
Rain barrels and cisterns collect building runoff from roof downspouts and store it for later reuse for non-potable applications such as irrigation.
Rain barrels and cisterns are low-cost water conservation devices that reduce runoff volume and, for very small storm events, delay and reduce the peak runoff flow rates.
Stormwater Management Objectives
Rain barrels are most often used for individual residences, while cisterns have both residential and commercial applications. Both storage devices act to decrease the volume and flow rate of rooftop generated stormwater runoff. Rain barrels and cisterns can provide a source of chemically untreated 'soft water' for gardens and compost and other non-potable needs, free of most sediment and dissolved salts.
Rain barrels are most effective when collected rainwater is emptied from the barrel prior to the next storm event. Rain barrel water is most commonly used for residential landscaping purposes.
Peak discharge is minimally impacted by the use of rain barrels and cisterns. An initial runoff volume is retained by the storage devices, ranging from approximately 50 gallons to several thousand for each device, prior to the remaining runoff bypassing the systems. When used throughout a watershed or stormwater collection basin, rain barrels and cisterns will modestly impact the peak stormwater flow rate.
Modest water quality improvements will be gained by using rain barrels and cisterns to reduce the volume of stormwater available to convey pollutants. The removal effectiveness of rain gardens has been studied during field and laboratory studies conducted at the University of Maryland (Houng and Davis, 2009).
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- Houng Li and A.P. Davis. 2009. Water Quality Improvements through Reductions of Pollutant Loads Using Bioretention, Journal of Environmental Engineering, Vol. 135, No. 8, August 1, 2009.