New York City (NYC) draws its drinking water from three protected surface water systems: the Catskill, the Delaware and the Croton watersheds. The majority of NYC’s drinking water is supplied by the Catskill/Delaware watershed, located approximately 100 miles outside the city. Historically, NYC had not filtered the water from this system nor did they require any additional barriers to microbial contaminants due to the pristine nature of the watershed. The total area of both watersheds is approximately 1,972 square miles and contains 19 reservoirs and three controlled lakes.
In 2006, the United States Environmental Protection Agency (EPA) released the Long Term Enhanced Surface Water Treatment Rule (LT2ESWTR). This rule required unfiltered surface water plants to install treatment to inactivate Cryptosporidium. Engineers working on the Catskill/Delaware project evaluated a new filtration plant, but the cost of installing a two billion gallon per day (BGD) filtration facility was significantly greater than other alternatives. After evaluation of available technologies, it was decided that UV was the most practical and cost-effective solution.
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