Dalecarlia Water Treatment Plant, District of Columbia

The Dalecarlia Water Treatment Plant, located at DC’s most upstream point on the Potomac, cleans the water that comes into it from the adjacent Dalecarlia Reservoir, which is the primary drinking water reservoir for Washington DC. The 50 acre reservoir spans the boundary between DC and Maryland, and is filled by two pipelines bringing water to it from the Potomac River. One is less than a mile long, and connects to an intake on the River at Little Falls Dam, which was constructed in 1959, to enhance the water intake for the City. The other connects to an intake at Great Falls Dam, several miles further up the Potomac. This intake is connected to the reservoir by the 12 mile long Washington Aqueduct, which was one of the nation’s earliest major aqueducts, commissioned by Congress in 1852, to deal with the putrid water of the Capital. The aqueduct travels in a pipe under Macarthur Boulevard, from Great Falls, to the Dalecarlia Reservoir. Some water leaves the reservoir untreated and goes to the Georgetown Reservoir and to the McMillan Reservoir, two additional reservoirs in DC, downstream.