the reservoir was completed in 1858 by the united states army corps of engineers as part of the washington aqueduct project. it began providing water on january 3, 1859. initially the reservoir provided water to the city from the adjacent little falls branch until the aqueduct construction was completed. regular water service from the potomac river source through the aqueduct commenced in 1864. the reservoir was modified in 1895 and 1935 to improve water quality and increase water supply.