Cities supplied primarily by surface water with water treatment Cities that rely on more or less polluted surface water from the lower reaches of rivers have to rely on extensive and costly water purification plants. The Las Vegas Valley obtains 90% of its water from Lake Mead on the Colorado River, which has been affected by drought. To supply a portion of the future water supply, Las Vegas plans to buy water rights in the Snake Valley in White Pine County, north of the city straddling the Utah border and other areas, pumping it to Las Vegas through a US$2 billion pipeline. Phoenix draws about half of its drinking water from the Salt River–Verde River watershed, and about 40% from the Colorado River further downstream at Lake Havasu through the Central Arizona Project. Los Angeles obtains about half of its drinking water from the Owens River and Mono Lake through the Los Angeles Aqueduct, with additional supplies from Lake Havasu through the Colorado River Aqueduct. San Diego imports nearly 90 percent of its water from other areas, specifically northern California and the Colorado River. The cities on the Mississippi River are supplied by water from that river except for Memphis. The metropolitan area of Atlanta receives 70% of its water from the Chattahoochee River and another 28% from the Etowah, Flint, Ocmulgee and Oconee rivers. Chicago is supplied by water from Lake Michigan and Detroit receives its water from the Detroit River. Philadelphia receives 60% of its water from the Delaware River and 40% from the Schuylkill River. Washington, D.C. receives its water from the Potomac River through the Washington Aqueduct. Cities supplied primarily by groundwater Miami and its metropolitan area obtain drinking water primarily from the Biscayne Aquifer. Given increasing water demand, Miami-Dade County is considering the use of reclaimed water to help preserve the Biscayne Aquifer. Memphis receives its water from artesian aquifers. San Antonio draws the bulk of its water from the Edwards Aquifer; it did not use any surface water until 2006. Cities supplied by a mix of groundwater and surface water Seventy-one percent of Houston's supply flows from the Trinity River into Lake Livingston, and from the San Jacinto River into Lake Conroe and Lake Houston. Deep underground wells drilled into the Evangeline and Chicot aquifers provide the other 29 percent of the city's water supply. Rainwater harvesting In the United States, until 2009 in