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.
Drinking water is one exposure route. These federal datasets also cover Suffolk County, NY.
The EPA places Suffolk County, NY in Zone 3 - the EPA's lowest-risk category, with a predicted average indoor radon level below 2 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
69% of homes in Suffolk County, NY were built before 1980, and 14% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Suffolk County, NY averages 6.7 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
Across 30 public water systems serving Suffolk County, NY with EPA lead testing on record, 3 (10%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.9 ppb. 14 water systems serving Suffolk County, NY carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule | 5 |
| Color | 4 |
| Manganese | 4 |
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 1 |
| PFOS | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.