Kensico Reservoir is located in Westchester County, about 3 miles north of White Plains and 15 miles north of New York City. Although formed by the damming of the Bronx River, it receives most of its water from the City’s west-of-Hudson reservoirs through the Catskill and Delaware Aqueducts. Kensico Reservoir consists of a western main basin and an eastern Rye Lake portion, with water passing freely between the two. It holds 30.6 billion gallons at full capacity and was placed into service in 1915.
The major function of Kensico Reservoir is to receive water from all six Catskill and Delaware system reservoirs, and to make those waters available for the fluctuating daily consumption demands of New York City. Ordinarily, Kensico Reservoir is the last stop for Catskill and Delaware system water before it enters two aqueducts and flows into the much smaller Hillview Reservoir in Yonkers (just north of the City line) for distribution throughout New York City. As such, it is called a terminal, rather than a collecting, reservoir. Under normal operations, water from the Catskill system’s Ashokan Reservoir and the Delaware system’s Rondout Reservoir travels through the Catskill and Delaware aqueducts and under the Hudson River to the Kensico Reservoir. (Delaware water usually passes through West Branch Reservoir before reaching Kensico Reservoir.) Kensico Reservoir also has its own watershed, which supplies just 2% or less of the total water volume entering the reservoir. As the final reservoir in the Catskill/Delaware system before water enters the distribution network, the Kensico Reservoir is subject to federal water quality standards for coliforms and turbidity.
The Kensico watershed’s drainage basin is 13 square miles and includes portions of the Towns of Harrison, Mount Pleasant, North Castle and a small part of Fairfield County, Connecticut.