In 1999 the American Water Works Association’s Research Foundation published a study of Residential End Uses of Water.
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They studied 1,188 homes in 12 sites, with 28,015 logged days of residential water use. They found that 42% of water use was indoor and 58% outdoor. While variations in water use depended on obvious factors such as lot size and climate, they also determined that:

  • Homes with in-ground sprinkler systems use 35 percent more water outdoors than those who do not have an in-ground system

  • Households that employ an automatic timer to control their irrigation systems used 47 percent more water outdoors than those that do not
  • Households with drip irrigation systems use 16 percent more water outdoors than those without drip irrigation systems

  • Households who water with a hand-held hose use 33 percent less water outdoors than other households

  • Households who maintain a garden use 30 percent more water outdoors than those without a garden

  • Households with access to another, non-utility, water source displayed 25 percent lower outdoor use than those who used only utility-supplied water

On average, homes with swimming pools are estimated to use more than twice as much water outdoors than homes without swimming pools, everything else held constant.”