The Washington Aqueduct is the District of Columbia's first public water system. Built by the Army Corps of Engineers from 1853 to 1863, it is a monumental achievement and a tribute to the brilliance of its designer and developer, Montgomery C. Meigs. In 1852 the ever-growing population of Washington, and the memory of two devastating fires, forced the U.S. Congress to acknowledge that the nation's capital required more than the wells and springs that were its current sources of water.
In November of 1853 ground was broken at Great Falls, Maryland for a public water system for Washington. Meig's plan was to divert the water from the Potomac River (12 miles upstream) into a brick conduit. Gravity and pumping stations would direct water through the conduit to retaining reservoirs where it could then be pumped to the city's pipelines.
In the mid-1920's a second conduit was added to increase the capacity of the system, and the intake was enlarged and modernized. The most recent expansion in the 1970's produced the building and observation deck that stand on the original location today. Four "gates" allow water diverted behind the dam to enter the two conduits by gravity flow. A small portion of the original sandstone intake is still visible on the shoreline.
Also see washingtonaqueduct.nab.usace.army.mil.