Environmental Prevents 76,000 gallons of annual stormwater runoff from entering the city's aging combined sewer system by collecting and reusing runoff from a 40,000 sf area of the courtyard and office building roof and reusing it in the courtyard for irrigation and water feature replenishment. Stormwater runoff in Washington, D.C. frequently exceeds the capacity of the combined sewer system. This overflow leads to periodic flooding of the National Mall and low-lying areas, and contributes to

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... llution of the region's rivers and streams. By capturing, collecting and reusing stormwater on site, runoff is prevented from entering the city's system, helping to reduce flooding and the problems it causes. None of the streetscaped areas are irrigated. Captured stormwater supplies all of the courtyard irrigation and replenishes the water feature. Stormwater is collected from the 40,000 ft 2 area of the office-building roof and the courtyard and directed into the filtration system and 7,500 gallon storage cistern located in the underground parking garage. Collected and filtered water is then pumped back to the courtyard for irrigation and to replace water lost to evaporation in the water feature. To determine the total amount of water reused annually, and therefore potable water saved, the amount of water needed per year for irrigation was added to the amount of water lost per year due to evaporation.