The beauty of New York City’s water supply is its simplicity relative to its size. It is a vast system, spread over 2,000 square miles of three watersheds, with reservoirs as far as 130 miles from the city. More than one billion gallons of water a day is delivered to almost nine million people throughout New York State via 6,500 miles of aqueducts, tunnels, and pipes. The vast majority of water travels to your home by gravity and is so clean that it does not need to be filtered.
Very few major American cities have unfiltered water: San Francisco, Seattle, Portland (Oregon), Boston, and New York City. New York’s is by far the largest unfiltered supply. This is changing, partially. Ninety percent of New York’s water will remain unfiltered, but water from the Croton watershed—the city’s smallest, located in Westchester and Putnam counties —will soon be filtered.
When completed, the Croton Water Filtration Plant in the Bronx will provide up to 290 million gallons a day of filtered water (up to 30% of the City’s water needs) and will ensure that the Croton system remains a reliable, viable part of New York City’s vast water infrastructure.
The beauty of the filtration plant is that when it is completed, you won’t see it. It is a piece of modern underground infrastructure. The landscape above it—the largest, continuous, intensive green roof in North America—will be returned to its prior use as a golf course and driving range and will also serve as a model for storm water and groundwater reuse.
After nearly two centuries of reliance on increasingly polluted public and private wells, New Yorkers celebrated the completion of the Croton Aqueduct that brought pure and abundant water from the Croton River in then-rural Westchester County. The twin urban scourges of disease and fire were banished and Croton became the model for American urban water supplies.
Calls to filter Croton water date back to the years of its construction, when some people questioned the sanitary habits of the Irish immigrant labor gangs. Serious filtration plans developed in the late 1890s,when some civic leaders believed Croton water had unhealthy color and odor; by 1911, plans had been made for a filtration plant at the Jerome Park Reservoir in the Bronx. Two years later, the plan was dead and quickly forgotten: Croton water, city officials and civic leaders finally agreed,was perfectly fine. It still is—most of the time.
Croton is the oldest, smallest, most suburbanized, and closest component of the city’s water supply. For three-quarters of a century, Croton was the city’s sole source of water. With the opening of the Catskill and Delaware watersheds west of the Hudson River in the first half of the 20th century, Croton supplies just 10% of the city’s water.
The filtration plant is a big hole in the ground, beneath 12 acres in the southeast corner Van Cortlandt Park. The site is just north of the Jerome Park Reservoir (at the top left corner of the above photo), which was the planned site for a filtration plant a hundred years ago.
When the filtration plant is complete, it will be mostly covered by an eco-friendly green roof featuring a driving range, new clubhouse, and other facilities for the public Mosholu Golf Course.
The plant will use a filtration system called Dissolved Air Flotation (DAF),which first treats water with a chemical solvent, then injects air bubbles that catch particles and float them to the surface, where they are skimmed off.
Sandhogs drill holes in the walls of the aqueduct for rock bolts, in preparation for connecting the aqueduct to the filtration plant.
Untreated Croton water will enter the plant through the 19th-century New Croton Aqueduct; treated Croton water will continue on its journey to the city via tunnels made with the most modern tunneling technology.
The plant will be able to treat up to 290 million gallons of water a day, approximately half of which will pass through this tunnel.