"A groundbreaking, multibillion-dollar watershed protection plan launched more than two decades ago by New York City and rural partners sufficiently protects the city’s drinking water supply from contamination, according to the findings of an expert panel.
Since 1997, New York City has spent some $2.5 billion on ecosystem protection in the Catskill and Delaware watersheds, the source of most of the city’s drinking water. The money has been put to good use: upgrading 42 wastewater treatment plants, buying out land to prevent development, and stabilizing stream channels to prevent erosion. The funds also replaced failing septic tanks, trapped pollutants in stormwater, and helped dairy farmers control nutrients and pathogens from their manure.
The investments in high-quality source water have been a relative bargain for the city. Together, these program components have forestalled the need to construct a water filtration plant, estimated to cost up to $10 billion, plus annual operating expenses of several hundred million dollars."