Early Manhattan settlers obtained water for domestic purposes from shallow, privately-owned wells. In 1677 the first public well was dug in front of the old fort at Bowling Green. In 1776, when the population reached approximately 22,000, a reservoir was constructed on the east side of Broadway between Pearl and White Streets. Water pumped from wells sunk near the Collect Pond, east of the reservoir, and from the pond itself, was distributed through hollow logs laid in the principal streets. In 1800 the Manhattan Company (now The Chase Manhattan Bank, N.A.) sank a well at Reade and Centre Streets, pumped water into the reservoir on Chambers Street and distributed it through wooden mains to a portion of the community. In 1830 a tank for fire protection was constructed by the City at 13th Street and Broadway and was filled from well water. The water was distributed through 12-inch cast iron pipes. As the population grew, the well water became polluted and the supply, which was supplemented by cisterns and water drawn from a few springs in upper Manhattan, became inadequate.
After exploring alternatives for increasing supply, in the early 1830's, the City decided to impound water from the Croton River, in what is now Westchester County, and to build an aqueduct to carry water from the newly-created reservoir to Manhattan. This aqueduct, known today as the Old Croton Aqueduct, had a capacity of about 90 million gallons per day (mgd) and was placed in service in 1842. The distribution reservoirs were located in Manhattan at 42nd Street (on the present-day site of the New York Public Library) and in Central Park south of 86th Street (discontinued in 1925). New reservoirs were constructed to meet the City's growing demand: Boyds Corner in 1873 and Middle Branch in 1878. Work began on a second aqueduct, called the New Croton Aqueduct, in 1885. Although not completed until 1893, it was placed in service in 1890. In 1898, the five-borough City of New York was formed with the consolidation of Manhattan, the Bronx, Brooklyn, Queens and Staten Island into a single entity. The various water systems in those communities became part of the New York City Water Supply System.
In 1905 the New York City Board of Water Supply was created by the State Legislature to identify and deliver new sources of water for the constantly-growing City. After careful study, the City decided to develop additional water sources from the valleys of the Catskill Mountains, north and west of the City. The Board of Water Supply proceeded to plan and construct the Ashokan Reservoir and Dam, which impounded the waters of the Esopus Creek in Ulster County, one of the four watersheds in the Catskills.
The water was carried to the City in the Catskill Aqueduct and delivered to water mains within the City through a huge water tunnel, known as City Tunnel 1. This project, the development of the first part of the Catskill Reservoir System, was completed in 1915. It was subsequently turned over to the City's Department of Water Supply, Gas and Electricity for operation and maintenance. The balance of the Catskill System, including the construction of the Schoharie Reservoir in Greene and Schoharie Counties, and the Shandaken Tunnel, which carries water from the Schoharie to the Esopus Creek where it flows into the Ashokan Reservoir, was completed in 1928. Even before the Schoharie Reservoir was ready for service, it was clear that new sources needed to be developed to serve the City.
In 1927 the Board of Water Supply submitted a plan to the City's Board of Estimate and Apportionment for the development of the upper portion of the Rondout watershed in Sullivan and Ulster Counties and tributaries of the Delaware River in Delaware County. This project was approved in 1928. Work was subsequently delayed by an action brought by the State of New Jersey in the Supreme Court of the United States to enjoin the City and State of New York from using the waters of any Delaware River tributary, regardless of its location. In May 1931, the Supreme Court of the United States upheld the right of the City to augment its water supply from the headwaters of the Delaware River. Construction of the Delaware system, which today provides 50% of the City's daily demand, was begun in March 1937. The Delaware system, in some places more than 125 miles from New York City, was placed in service in stages. The Delaware Aqueduct, a pressurized tunnel which carries water from the Delaware System Reservoirs under the Hudson River and into Boyds Corner, West Branch and Kensico Reservoirs in Putnam and Westchester Counties,was completed in 1944. The Neversink Reservoir was put into service in 1954; the Rondout Reservoir in 1954, the Pepacton Reservoir in 1955 and the Cannonsville Reservoir in 1964.
Today, New York City has the largest unfiltered surface water supply in the world. Every day, some 1.3 billions gallons of water from this vast system is delivered to eight million New York City residents, one million more consumers in four upstate counties and hundreds of thousands of commuters and tourists. The New York City Water Supply System includes a watershed of 1,969 square miles across eight counties north and west of the City: Westchester, Putnam and Dutchess on the east side of the Hudson River and Delaware, Greene, Schoharie, Sullivan and Ulster in the Catskill Mountains, west of the Hudson.
The system's 19 reservoirs and three controlled lakes contain a total storage capacity of 580 billion gallons. The three reservoir systems were designed and built with various interconnections to increase flexibility by permitting exchange of water from one to another. This feature mitigates localized droughts and takes advantage of excess water in any of the three watersheds.
In comparison to other public water systems, New York City's system is both economical and flexible. Approximately 95% of the total water supply is delivered to the consumer by gravity. Only about 5% of the water is regularly pumped to maintain the desired pressure. As a result, operating costs are relatively insensitive to fluctuations in the cost of power. When drought conditions exist, additional pumping is required.