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New York City's water supply system is one of the most extensive municipal water systems in the world. This complex system relies on a combination of tunnels, aqueducts, and reservoirs to meet the daily needs of the city's over 8 million residents and its many visitors. Thanks to well-protected wilderness watersheds, New York's water treatment process is simpler than in other American cities. One advantage of the system is that 95% of the total water supply is supplied by gravity. The other 5% needs to be pumped to maintain pressure, but this is sometimes increased in times of drought when the reservoirs are at lower than normal levels.
The city has sought to restrict development throughout its watershed. One of its largest watershed protection programs is the Land Acquisition Program, under which the New York City Department of Environmental Protection (DEP) has purchased or protected through conservation easement over 130,000 acres (53,000 ha) since 1997.
Responsibility for the city water supply is shared between three institutions: The DEP operates and maintains the system and is responsible for investment planning; the Municipal Water Finance Authority raises debt in the market to finance the system; and the Water Board sets rates and collects user payments.
The DEP has a workforce of over 6,000 employees. It includes three bureaus in charge of, respectively, the upstate water supply system, the city's water and sewer operations, and wastewater treatment:
The New York City Municipal Water Finance Authority (“NYW”) finances the capital needs of the water and sewer system of the city through the issuance of bonds, commercial paper and other obligations. It is a public-benefit corporation created in 1985 pursuant to the New York City Municipal Water Finance Authority Act. The Authority is administered by a seven-member Board of Directors. Four of the members are ex officio members: the Commissioner of Environmental Protection of the City, the Director of Management and Budget of the City, the Commissioner of Finance of the City and the Commissioner of Environmental Conservation of the State. The remaining three members are public appointments: two by the Mayor, and one by the Governor.
The New York City Water Board sets water and sewer rates for New York City sufficient to pay the costs of operating and financing the system, and collects user payments from customers for services provided by the water and wastewater utility systems of the City of New York. The five Board members are appointed to two-year terms by the Mayor.
The city water system consists of reservoirs, aqueducts, tunnels and distribution pipes that channel drinking water to residents. A comprehensive raised-relief map of the system is on display at the Queens Museum of Art.
The water system has a storage capacity of 550 billion US gallons (2.1×109 m3) and provides over 1.2 billion US gallons (4,500,000 m3) per day of drinking water to more than eight million city residents and another one million users in four upstate counties bordering on the water supply system. Three separate sub-systems, each consisting of reservoirs and aqueducts, bring water from Upstate New York to the city:
The latter two aqueducts provide 90 percent of the drinking water of the city. Water from both aqueducts is stored first in the large Kensico Reservoir and subsequently in the much smaller Hillview Reservoir closer to the city.
From the Hillview reservoir water flows by gravity through three tunnels under the city, where water rises again to the surface under natural pressure through a number of shafts. The three tunnels are:
The distribution system is made up of an extensive grid of water mains stretching approximately 6,500 miles (10,500 km).
In order to comply with federal and state laws regarding the filtration and disinfection of drinking water, the U.S. Environmental Protection Agency (EPA) and the New York State Department of Health called on the city to create a treatment plan to serve the Croton System. The underground filtration plant is under construction in Van Cortlandt Park. While the Bloomberg administration originally budgeted the project at $992 million in 2003, an audit by the city's comptroller placed the actual costs at $2.1 billion in August 2009.
The New York City water supply system leaks at a rate of up to 36 million US gallons (140,000 m3) per day. A complex five-year project with an estimated $240 million construction cost was initiated in November 2008 to correct some of this leakage.
The construction of Water tunnel No. 3 is intended to provide the city with a critical third connection to its Upstate New York water supply system, allowing the city to close tunnels No. 1 and No. 2 for repair for the first time of their history. The tunnel will eventually be more than 60 miles (97 km) long. Construction on the tunnel began in 1970, and its first phase is completed. Completion of all phases is not expected until at least 2020.