90% of the water supply for New York City comes from sources in the Catskill Mountains, northwest of the city. Stored in reservoirs which dam streams which drain the watersheds of the mountains, the water is transported by aqueducts to the city. In 2007, the water from the Catskills was declared by the Environmental Protection Agency to be pure enough to be exempt from filtration requirements. The remaining water, from the Croton Watershed, immediately north of the city, in developed Westchester County, requires filtration. The city has budgeted $300 million for land acquisition and other measures to protect the watershed during the next 10 years. In 2007, 31% of the watershed, partly state forest, was protected from development. 
The possibility of drilling for gas in the watersheds used by New York City, a process which may involve injection of chemically treated water to crack shale formations has raised fears of contamination of underground water.
- ↑ "City’s Catskill Water Gets 10-Year Approval", article by Anthony DePalma in the New York Times, April 13, 2007
- ↑ "Putting Water Ahead of Natural Gas" article by Peter Applebome in The New York Times August 9, 2008
- Water-Works: The Architecture And Engineering of the New York City Water Supply by Paul Deppe, Peter H. Gleick, Albert F. Appleton, Gina Pollara, Kevin Bone; Monacelli Press (December, 2006), hardcover, 268 pages, ISBN 1580-93176-6 ISBN 978-1580-93176-2
- "Plumber’s Job on a Giant’s Scale: Fixing New York’s Drinking Straw" article by Ken Belson in The New York Times November 22, 2008