As reported in ENR on June 2, 2014

Constructed to serve the residents of New York City (NYC), the $1.3-billion Catskill/Delaware Ultraviolet Light Disinfection Facility (Cat/Del) employs 56 UV units, each with a 40 million MGD capacity. This makes them the largest UV’units built to date.The Joint Venture team of Skanska, ECCO III Enterprises, Inc. and J.F. White Contracting Co. completed construction of the facility. “This represents a tremendous leap forward in water treatment technology, it is by far the largest water treatment plant of its kind in the world. The second largest U.S. installation in operation treats less than one-third of the capacity of the Cat/ Del UV Facility, which safely treats and controls the flow of more than 2 billion gallons of drinking water per day” as told to ENR by Keith Chouinard, Senior Vice President of Operations, Skanska USA Civil Northeast

The NYC water system is the largest unfiltered surface water system in the U.S., delivering water to 9 million customers and conveying this volume entirely by gravity.