Lying on the western part of the Delaware Watershed, it is the westernmost of New York City's reservoirs.

Its 455 square miles (1,180 km2) drainage basin is the largest of all of the NYC reservoirs.

Water from the reservoir flows through the 44-mile (71 km) West Delaware Tunnel into the Rondout Reservoir, before joining the 85-mile (137 km) Delaware Aqueduct, which provides New York City with about 50% of its drinking water.

The Delaware Aqueduct then crosses beneath the Hudson River and continues on to the West Branch Reservoir in Putnam County, New York, then the Kensico Reservoir in Westchester County, both north of the city.

It then continues further south to the Hillview Reservoir in Yonkers, where it joins the flows of the Catskill and New Croton aqueducts for distribution through the New York City tunnel system.