This article presents an analysis of the projected performance of urban residential rainwater harvesting systems in the United States (U.S.). The objectives are to quantify for 23 cities in seven climatic regions (1) water supply provided from rainwater harvested at a residential parcel and (2) stormwater runoff reduction from a residential drainage catchment. Water-saving efficiency is determined using a water-balance approach applied at a daily time step for a range of rainwater cistern sizes. The results show that performance is a function of cistern size and climatic pattern. A single rain barrel (190 l [50 gal]) installed at a residential parcel is able to provide approximately 50% water-saving efficiency for the nonpotable indoor water demand scenario in cities of the East Coast, Southeast, Midwest, and Pacific Northwest, but <30% water-saving efficiency in cities of the Mountain West, Southwest, and most of California. Stormwater management benefits are quantified using the U.S. Environmental Protection Agency Storm Water Management Model. The results indicate that rainwater harvesting can reduce stormwater runoff volume up to 20% in semiarid regions, and less in regions receiving greater rainfall amounts for a long-term simulation. Overall, the results suggest that U.S. cities and individual residents can benefit from implementing rainwater harvesting as a stormwater control measure and as an alternative source of water.

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Bioretention as sustainable urban stormwater management has gathered much recent attention, and implementation is expanding in mesic locations that receive more than 1,000 mm of annual precipitation. The arid southwestern United States is the fastest growing and most urbanized region in the country. Consequently, there is a need to establish design recommendations for bioretention to control stormwater from expanding urban development in this ecologically sensitive region. Therefore, we review the ecological limits and opportunities for designing bioretention in arid and semiarid regions. We incorporated USEPA Stormwater Management Model (SWMM) simulations to synthesize ecologically based design recommendations for bioretention in arid climates. From our review, an ideal bioretention garden area should be 6 to 8% of the contributing impervious drainage area (depending on region) with two layers of media, a 0.5‐m low‐nutrient topsoil layer above a 0.6‐m porous media layer that acts as temporary storage during a storm event. When planted with the suggested vegetation, this design maximizes stormwater treatment by promoting ecological treatment in the topsoil while promoting infiltration and evapotranspiration of stormwater by deep‐rooted shrubs that require no irrigation after establishment. This synthesis improves water resources management in arid and semiarid regions by introducing a sustainable bioretention design that protects local surface waters while reducing regional water demands for irrigation.

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