Before it goes anywhere, the city’s drinking water starts out in three major watersheds — the Delaware and Catskill systems west of the Hudson River and the Croton system just north of the city. In 2017, New York City got about 97 percent of its water from the Catskill/Delaware systems and about 3 percent from the Croton system, the DEP said.
The watersheds feed more than a dozen reservoirs and controlled lakes. The largest reservoir, the Pepacton, has a capacity of 140 billion gallons. The Ashokan in Ulster County, pictured, has a capacity of 123 billion gallons.
Officials take measurements throughout the reservoirs, looking at things like turbidity (water clarity) and contaminants, to select the highest quality water available at that moment to be released downstate.
The water supply is so critical to the city that a dedicated police force with more than 200 members works 24 hours a day to prevent illegal dumping and other misuses of the waterways. During Hurricane Irene, the DEP Police were even called on to conduct water rescues.
Next, the water flows from the reservoirs and lakes through a system of aqueducts and tunnels. These include the 100-year-old Catskill Aqueduct, which extends 92 miles from the Ashokan Reservoir in the Catskill Mountains to the northern boundary of the city, and relies solely on gravity to carry the water. When it was completed in the early 1900s, the Catskill Aqueduct was considered by some as an engineering feat on the level of the Panama or Suez canals.
The 85-mile Delaware Aqueduct to its southwest is much newer, having been completed in the mid-1940s. The Delaware is so large that a two-man submarine has been used to inspect it for leaks. There are other aqueducts and tunnels, too. They all give the system a cascading effect, letting the water flow downstate.
After traveling southeast through the Catskill and Delaware aqueducts, water arrives at the Kensico Reservoir about three miles north of White Plains in Westchester County. The reservoir is an important balancing reservoir for the daily demands of the city. Up until this point, the water has also been unfiltered and untreated. But now it gets treated with fluoride and disinfected at what is considered the world’s largest ultraviolet treatment facility, as seen above. The UV treatment is especially useful for zapping Cryptosporidium and Giardia, which are not the names of punk bands but potentially harmful microorganisms.
The water makes another stop on its southerly voyage to the city: Hillview Reservoir in Yonkers. The DEP says the reservoir serves three critical functions. First, it balances daily demand (water consumption peaks twice during the day, in the morning and at night when people are home); second, water undergoes additional disinfection. And third, the reservoir serves to elevate the water so that when it does continue on, gravity propels it with enough force to flow into homes.
From the aqueducts, water is distributed throughout the city via three tunnels — No. 1 was put into service in 1917 and No. 2 has been in service since 1936. Tunnel No. 3, pictured, began serving the Bronx and upper Manhattan in 1998, and an extension into lower Manhattan was activated in 2013. Construction, which began in 1970 at a cost of about $5 billion, continues on the Brooklyn and Queens portions. Water then gets routed to distribution mains and then …
Finally, the water arrives in your home. If your building is less than six stories high, gravity does all the work. If not, then pumps in your building will help to move the water to the top floors. To maintain quality, testing is done at nearly 1,000 sampling stations around the city.
How good is the water that comes out of your faucet? Here’s one way to look at it: The city is only one of five big municipalities that is allowed by the federal government to supply unfiltered water. If that’s not enough, the DEP releases a yearly Water Quality Report offering information on the water supply. You can read the full 2017 report at nyc.gov/html/dep/pdf.