New York City’s drinking water travels up to 125 miles from a vast network of 19 reservoirs and three controlled lakes spread across the Catskill Mountains and the Hudson Valley. The entire system holds roughly 580 billion gallons of water and delivers about 1 billion gallons per day to more than 8 million residents. Three separate watershed systems feed the city, each built in a different era and covering a different stretch of upstate New York.
The Three Watershed Systems
NYC’s water comes from three distinct supply systems: Catskill, Delaware, and Croton. Each draws from different geography, and together they provide overlapping capacity so the city isn’t reliant on any single source.
The Delaware System is the workhorse, supplying about 50 percent of the city’s water on an average day. Its four reservoirs, Pepacton, Cannonsville, Neversink, and Rondout, sit in the western Catskill region and hold a combined 322 billion gallons. Pepacton is the largest single reservoir in the entire system at 140.2 billion gallons. Water from all four reservoirs funnels into the Rondout Reservoir before heading south through the Delaware Aqueduct.
The Catskill System adds another major share. The Schoharie Reservoir (17.6 billion gallons) feeds into the much larger Ashokan Reservoir (122.9 billion gallons) in Ulster County. From there, water travels 92 miles through the Catskill Aqueduct, passing under the Hudson River through a deep siphon, before reaching the Kensico Reservoir in Westchester County. Kensico acts as a mixing and settling point where water from both the Catskill and Delaware systems comes together before moving toward the city.
The Croton System is the oldest of the three, with 12 reservoirs and three controlled lakes located primarily in Westchester and Putnam Counties. It can supply up to 30 percent of the city’s daily needs, giving the system critical backup capacity.
How the Water Gets Treated
One of the more remarkable things about NYC’s water supply is that the Catskill and Delaware systems are among the largest unfiltered surface water supplies in the country. Instead of running through a traditional filtration plant, water from these two systems is disinfected using ultraviolet light at a facility in Westchester County. That UV plant can treat up to 2 billion gallons per day, making it one of the largest UV disinfection facilities in the world. Inside, 56 treatment units each hold 210 UV bulbs that neutralize harmful microorganisms as water passes through.
The city can skip conventional filtration for these two systems because the upstate watersheds are carefully protected. Forested land surrounds the reservoirs, and strict land-use regulations limit development and pollution sources in the catchment areas. This approach, protecting the source rather than filtering after the fact, has saved the city billions of dollars compared to building a filtration plant large enough to handle the Catskill and Delaware supply.
The Croton system is a different story. Because its watersheds are closer to developed suburban areas, the water requires full filtration. The Croton Water Filtration Plant, a 400,000-square-foot facility built beneath Van Cortlandt Park in the Bronx, handles that job. It can filter up to 290 million gallons per day. Construction began in 2004, and the plant was activated in 2015, reintroducing Croton water into the city’s distribution network after a years-long gap.
Beyond UV treatment and filtration, the city adds fluoride at a concentration of about 0.7 milligrams per liter, in line with New York City Health Code requirements. Scientists test the drinking water hundreds of times every day, collecting samples from reservoirs, aqueducts, treatment facilities, and 1,000 street-side sampling stations across all five boroughs.
The Journey From Reservoir to Tap
Water from the Catskill and Delaware systems converges at the Kensico Reservoir in Westchester County, where it gets UV treatment. From Kensico, it flows to the Hillview Reservoir in Yonkers, a small balancing reservoir (0.9 billion gallons) that has served as the distribution gateway since 1915. Hillview feeds the city’s network of underground tunnels and mains that branch out to homes and businesses across all five boroughs.
The entire journey relies on gravity. The reservoirs sit at higher elevations in the Catskills, and the aqueducts slope gradually downhill toward the city. No massive pumping stations are needed to push the water along for most of its trip, which keeps operating costs lower than systems that depend on energy-intensive pumps.
Leaks and Repairs in the Delaware Aqueduct
The Delaware Aqueduct, the tunnel that carries water from the Rondout Reservoir to the city, has been leaking since at least the 1990s. Two sections of the Rondout-West Branch Tunnel, near the towns of Wawarsing in Ulster County and Roseton in Orange County, lose a combined 35 million gallons of water per day. That’s roughly 3.5 percent of the city’s daily consumption simply seeping into the ground.
Fixing the problem has been one of the largest infrastructure projects in the city’s history. The Wawarsing section can be repaired from inside the existing tunnel, but the Roseton crossing required a completely new bypass tunnel to route water around the leaking segment. The project also demanded preparation for a full shutdown of the aqueduct while crews connect the bypass to the existing system. To keep water flowing during that shutdown period, the city planned a series of backup measures: boosting the Catskill Aqueduct’s capacity, reactivating a groundwater system in Queens, and establishing emergency interconnections with water systems in New Jersey and Nassau County.
How Much Water NYC Uses
In 2024, New York City consumed an average of about 1,002 million gallons per day, serving a population of roughly 8.5 million people. That number has actually dropped significantly over the past few decades thanks to conservation efforts, low-flow fixtures, and leak detection programs. In the 1980s, daily consumption regularly exceeded 1.5 billion gallons.
With 580 billion gallons of total storage capacity, the system theoretically holds enough water to supply the city for well over a year even if no rain fell, though in practice reservoir levels fluctuate with seasonal rainfall and snowmelt patterns. The combination of three independent supply systems, massive storage reserves, and gravity-fed delivery makes NYC’s water infrastructure one of the most resilient municipal systems in the United States.