Delaware Aqueduct (dĕl`əwâr, –wər), SE N.Y., 85 mi (137 km) long, carrying water from the Rondout Reservoir, Sullivan co., SE into the New York City water system at the Hillview Reservoir, Westchester co.; built 1937–62. The tunnel taps the Delaware River basin and supplies more than half of New York City's water. The aqueduct's deep, gravity-flow construction requires little maintenance. The Rondout Reservoir receives water from other Delaware basin reservoirs through a tunnel system. In 1965 the aqueduct was extended; its total distance is now 105 mi (170 km).