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 8 million residents and 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 system is divided into three separate sub-systems:
The Catskill aqueduct, built decades later, is significantly larger than the Croton. In the early years of the 20th century, the city and state designated thousands of acres of land in the eastern Catskill Mountains to build two reservoirs that more than doubled the city's capacity.
In the 1950s and 1960s, the city expanded its water system again, tapping the east and west branches of the Delaware River, as well as other tributaries of the Delaware and Hudson rivers to create the newest and largest of its three systems, the Delaware system, which provides around half of the city's water supply.