THE city of New York draws practically its entire water supply from three great reservoir systems, the Croton, Catskill, and Delaware. In the early 1900s, pollution of the drinking water from local springs pushed the city to purchase water rights along the Croton River in Westchester County, according to the Department of Environmental Protection. The city's first aqueduct, built of stone and brick masonry and based on designs of the ancient Romans, went into service in 1842. It was more than 30 miles long and provided a supply of 60 million gallons a day.
A new Croton Aqueduct, three times as large as the old one and following a completely different route, was completed in 1893. The Croton system conveys 10 percent of the city's water.
A severe drought that left the city with only a five-day supply of water prompted the construction of the Catskill system. That system now pipes 40 percent of the city's water from two major reservoirs. It first came into use in 1915, when water flowed through a 92-mile section from the Ashokan Reservoir through the Catskill Aqueduct to the city.
Water engineers knew as early as the 1920s that New York's growing population would need a third system. But litigation and World War II delayed completion of the Delaware system until 1967. The Delaware reservoirs now safely yield about 580 million gallons of water per day.