New York City Drinking Water Supply System

The New York City water supply system utilizes three separate systems of reservoirs, which obtain water from some 2,000 square miles of watershed in upstate New York. The three systems include the Croton System, the Catskill System and the Delaware System. The three elements of the New York City delivery system represent separate systems without direct inter-connections. Two tunnels City Tunnel No. 1 and No. 2 carry water from the Croton System to New York City. The Richmond Tunnel carries water from City Tunnel No. 2 to Staten Island. A new tunnel, City Tunnel No. 3, has been under construction since 1970. Most of the work in Manhattan and the Bronx has been completed. Tunneling is underway in Brooklyn and Queens.

Today, 50% of the city’s water comes from the Delaware system, 40% from the Catskill system, and the remaining 10% comes from the Croton system. The city now has 19 reservoirs; the farthest is 120 miles from central Manhattan. This long travel time, which is powered by gravity, results in most of the microbes dying naturally. The water is treated with:

chlorine to kill organisms,
fluoride to prevent
tooth decay,
sodium hydroxide to raise pH levels, and
orthophosphate, a substance that coats pipes, to prevent lead from leaching into the drinking water.

The Croton System is the oldest controlling flow from 12 reservoirs and five lakes which covers about 370 square miles of the Croton River Drainage Basin. The average yield of the system is 300 million gallons per day (MGD). The Catskill System consists of two reservoirs, the Ashokan and the Schoharie. The Ashokan Reservoir impounds water from 247 square miles of the drainage and the Schoharie Reservoir impounds water from the 314 square mile drainage basin. The Ashokan and Schoharie Reservoirs drain into the Catskill Aqueduct with a capacity of 550 MGD. The Delaware System consists of three reservoirs located in the Delaware River Basin, the Canonsville, Pepacton and Neversink Reservoirs, and the Rondout Reservoir on Rondout Creek in the Hudson River Basin. The safe yield of the entire Delaware water system is 610 MGD. (New York City Water Supply)