of the Sudbury River was impounded creating Lake Cochituate, from where the Cochituate Aqueduct transported water to the Brookline Reservoir that fed the city's distribution system. In 1853, Washington, D.C., followed suit by beginning the construction of the Washington Aqueduct to provide water from the Great Falls on the Potomac River. In 1854, the British physician John Snow found that cholera was spread through contaminated water. As a result of his findings, several cities began to treat all water with sand filters and chlorine before distributing it to the public. Before efforts to clean drinking water were implemented at the turn of the 20th century, mortality among 1- to 5-year-olds in the United States in some major river cities was nearly one in five. Clean water is estimated to have reduced about three-fourths of infant mortality, and two-thirds of child mortality. By 1900, sand filtration was widely used. In 1908, the first continuous application of chlorination to drinking U.S. water was in Jersey City, New Jersey (and not without controversy). Cities also began to construct sewers in the late 19th century. As a result of water treatment and sanitation, the incidence of cholera and typhoid rapidly decreased. Slow sand filtration was initially the technology of choice for water treatment, later being gradually displaced by rapid sand filtration. As a result of the water purification efforts, mortality among black infants declined in particular, leading to a 13 percent reduction in the black-white infant mortality gap. In the arid American Southwest, the water demand of rapidly growing cities such as Los Angeles exceeded local water availability, requiring the construction of large pipelines to bring in water from far-away sources. The most spectacular example is the first Los Angeles Aqueduct built between 1905 and 1913 to supply water from the Owens Valley over a distance of 233 mi (375 km). Drinking water quality standards were first issued in 1914 by the United States Public Health Service. However they were only enforceable for interstate transportation carriers (such as railroads) at specific points where water was transferred. Sanitation until 1948 Most of the first sewer systems in the United States were built as combined sewers (carrying both storm water and sewerage). They discharged into rivers, lakes and the sea without any treatment. The main reason for choosing combined sewers over separate systems (separating sanitary sewers from storm water drains) was a belief that combined sewer