Through the early 21st century, the three aqueduct systems that supply water to the city utilized chlorination technology, but not filtration (unlike other large municipal water systems in the US). The water in the Croton Aqueduct system, the oldest of the three, often had high turbidity levels, which limits the effectiveness of chlorination as a disinfection process.[8] The turbidity problems in the Croton Watershed come from naturally occurring sources and urban runoff pollution. The Croton system supplies about ten percent of the New York City water system[9] and building a filtration system to address the turbidity problems had been proposed since the 1990s.[6]
The Croton filtration plant was built after a lawsuit was filed in 1997 against the City of New York by the U.S. Environmental Protection Agency (EPA), the U.S. Department of Justice and the State of New York.[10] The city settled the suit and a consent decree was issued with the condition that the city would build the plant by 2006.[9] The city had been studying possible sites for such a plant for more than 20 years in both the Bronx and nearby Westchester County. The plant protects the public from Giardia and Cryptosporidium, microorganisms which can cause serious health problems.[2] The project was spearheaded by then Commissioner Christopher O. Ward. [11]
Raw water is delivered to the filtration plant by the New Croton Aqueduct and the Jerome Park Reservoir.[2] The Croton plant has a capacity of 320 million U.S. gallons (1.2 billion liters) per day and is designed to remove 99.9% of Giardia cysts, Cryptosporidium, and viruses. The system uses conventional drinking water treatment technologies:
The filtration plant was originally projected to cost $800 million,[3] but the project experienced delays and ballooning costs due to objections from the local community,[7] which required the city to propose alternate sites for such a plant.[12]
To lessen the disruption caused by the plant's construction, in 2010 the city used mitigation funds from the construction budget to restore the Van Cortlandt Park Parade Ground.[15][16] The Sachkerah Woods Playground, located at the park's southeast corner near the Mosholu Golf Course, was also built using Croton mitigation funds.[17]
The new plant allowed the city to provide greater capacity for its water system.[6] This was especially important since the city was preparing to shut off part of the Delaware Aqueduct in 2022[18][6] allowing the completion of a tunnel that would bypass a leaking section of the aqueduct in Newburgh, New York.[19]