Nassau County, New York: drinking water report. Nassau County occupies the western portion of Long Island, home to about 1.4 million residents.
Nassau County occupies the western portion of Long Island, home to about 1.4 million residents. Like neighboring Suffolk County, Nassau relies entirely on groundwater – there is no connection to New York City's upstate reservoir system. Over 50 water districts serve the county, each operating wells that tap the Upper Glacial, Magothy, and Lloyd aquifers beneath Long Island.
Nassau County shares Long Island's well-documented groundwater contamination legacy. Decades of industrial activity – particularly at former Grumman aerospace facilities in Bethpage – left volatile organic compounds and PFAS in the aquifer. The Bethpage Community Park Superfund site and the Navy-Grumman plume are among the most significant groundwater contamination sites in the northeastern United States.
New York State's PFAS MCLs of 10 ppt for PFOA and PFOS have required aggressive action from Nassau County water districts. According to the Nassau County Department of Public Works, over $200 million has been invested in PFAS treatment infrastructure across the county since 2019. UCMR5 data confirms ongoing detections in dozens of county systems despite treatment efforts.
Nassau County is investing heavily in treatment, but individual wells may still show elevated readings depending on proximity to contamination sources.
Check your water to see data for your specific water district. Even with utility-level treatment, a reverse osmosis filter provides an additional layer of household protection. Our water filter guide ranks systems by performance. Pull your detailed report, and visit our New York page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Nassau County, NY.
The EPA places Nassau 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.
86% of homes in Nassau County, NY were built before 1980, and 33% 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 Nassau County, NY averages 7.3 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 58 public water systems serving Nassau County, NY with EPA lead testing on record, 4 (6.9%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 3 ppb. 12 water systems serving Nassau County, NY carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Revised Total Coliform Rule | 2 |
| Lead and Copper Rule | 2 |
| PFOA | 2 |
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 1 |
| Iron | 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.