The Catskill-Delaware Ultraviolet (UV) Disinfection Facility is the largest UV water treatment plant in the world. This facility was just selected by Engineering News-Record (ENR) as a 2013 "Best of the Best Projects" winner.
New York City Department of Environmental Protection’s UV water treatment plant is located in Westchester County. It uses 56 low-pressure, high-output UV reactors to treat as much as 2 billion gallons of water a day.
Construction of this huge project began in the fall of 2008. On its completion four years later it became the world’s largest UV water treatment facility. In October, 2013, ENR selected it as the recipient of "New York's 2013 Best Projects Award." Yesterday they awarded it the 2013 "Best of the Best Projects" overall.
According to Water World “New York City's water supply is the largest unfiltered system in the nation. Likewise, the city's three watersheds (Catskill, Delaware, and Croton) extend 125 miles and include 19 reservoirs and three controlled lakes; the Catskill and Delaware watersheds supply 90 percent of the city's drinking water.” This project effectively eliminates the need for a multi-billion dollar water filtration plant for New York City's water supply.
A large portion of the Catskill Mountain region is within New York City’s watershed, and many communities in the Hudson Valley tap into the aqueduct system for their municipal water supply. Portions of the nearly 100 year old Catskill Aqueduct are currently under repair or being reconfigured to update the aging infrastructure. (From the reprint of the 1917 book “Water For New York City”.)