Suffolk County, New York: drinking water report. Suffolk County occupies the eastern two-thirds of Long Island, home to about 1.5 million residents.
Suffolk County occupies the eastern two-thirds of Long Island, home to about 1.5 million residents. Unlike New York City, Suffolk relies almost entirely on groundwater – drawing from the Upper Glacial, Magothy, and Lloyd aquifers beneath Long Island. The county has no connection to the city's upstate reservoir system. Over 50 water districts and private utilities serve the county, each operating independent well systems and treatment facilities.
Long Island has one of the most well-documented groundwater contamination problems in the northeastern United States. Decades of pesticide use, industrial activity, septic system discharge, and military operations at former Grumman facilities and Brookhaven National Laboratory have left a legacy of contaminants in the aquifers. The EPA's UCMR5 data shows PFAS detections in over 30 Suffolk County water systems.
New York State's aggressive PFAS MCLs of 10 ppt for PFOA and PFOS have forced several Suffolk County water districts to install treatment systems. According to the Suffolk County Water Authority, the county invested over $100 million in granular activated carbon treatment facilities between 2020 and 2025 to address PFAS contamination.
Suffolk County's sole-source aquifer designation means there is no backup supply. Protecting and treating groundwater is the only option.
Check your water to see monitoring data for your specific water district. If PFAS levels are elevated, a reverse osmosis or activated carbon filter adds household-level protection on top of utility treatment. Our water filter guide ranks filters by verified performance. Pull your detailed report, and visit our New York page for statewide patterns.