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Long Island NY Water Quality: PFAS Plumes, Navy Contamination, and an Aging Aquifer

March 23, 2026
Aerial view of Long Island New York coastline

Long Island is home to 2.8 million people across Nassau and Suffolk counties, and every single one of them depends on a sole-source aquifer for their drinking water. There are no reservoirs, no river intakes, no backup plan. Whatever seeps into the ground eventually reaches the water supply.

That geological reality makes Long Island one of the most vulnerable water systems in the United States — and decades of military activity, industrial manufacturing, and suburban development have left their mark.

The Sole-Source Aquifer

The EPA designated Long Island’s aquifer system as a “sole source” in 1978, meaning it supplies at least 50% of the drinking water for the area and there are no reasonably available alternative sources. In Long Island’s case, it supplies effectively 100%.

The system consists of three main layers: the Upper Glacial aquifer, the Magothy aquifer, and the Lloyd aquifer. Most public supply wells draw from the Magothy, which sits between 200 and 1,000 feet below the surface. But contamination that enters through the Upper Glacial layer can — and does — migrate downward over time.

PFAS: The Defining Contamination Issue

PFAS contamination on Long Island is extensive. Multiple sources have contributed to widespread contamination of the aquifer:

Military installations are among the worst offenders. The former Naval Weapons Industrial Reserve Plant in Bethpage and Grumman Aerospace’s manufacturing facilities created one of the most significant groundwater contamination plumes in the Northeast. The Bethpage Community Park plume contains volatile organic compounds and PFAS stretching for miles underground.

Republic Airport in Farmingdale and various fire training facilities have added AFFF-related PFAS to the mix.

Industrial sites across both counties — from dry cleaners to manufacturing plants — have contributed solvents, heavy metals, and emerging contaminants over decades.

Water contamination lawsuits have been a recurring feature of Long Island’s legal landscape, with a fresh wave of cases filed in 2025 and 2026 as testing reveals the true scope of PFAS contamination.

What the Testing Shows

Long Island water districts have been finding PFAS at concerning levels across both counties. Several public water supply wells have been shut down or fitted with treatment systems after testing revealed PFAS above New York’s maximum contaminant levels.

New York State set MCLs of 10 ppt for both PFOS and PFOA in 2020 — among the strictest in the nation. Many Long Island wells were above those limits before treatment was installed.

Key contaminants detected in Long Island’s water supply include:

The Septic System Problem

Here’s something most people don’t consider: roughly 360,000 homes on Long Island still use septic systems rather than connecting to sewers. Those systems discharge nitrogen and other contaminants directly into the ground — which means directly into the aquifer.

Suffolk County has been particularly affected. Elevated nitrate levels in eastern Suffolk are directly linked to the density of septic systems. The county has been promoting nitrogen-reducing septic technology, but replacing hundreds of thousands of aging systems is a generational project.

What’s Being Done

Long Island water districts have invested heavily in treatment. Granular activated carbon (GAC) filters and ion exchange systems have been installed at dozens of wells to remove PFAS. The cost is staggering — individual treatment systems can run into the millions, and the ongoing operational costs fall on ratepayers.

The Bethpage Superfund site is undergoing active remediation under EPA oversight, but the plume continues to migrate. Community groups have pushed for more aggressive containment, and the site remains one of the most closely watched cleanup efforts in the region.

New York State’s 2020 drinking water standards for PFAS and 1,4-Dioxane forced many districts to upgrade treatment faster than they had planned. The state has provided some funding, but the burden has largely fallen on local water authorities.

What Residents Should Do

Whether you’re in Nassau or Suffolk County, here’s how to protect yourself:

  1. Check your water district’s testing results. New York requires public water systems to publish annual water quality reports. Look for PFAS, 1,4-Dioxane, and nitrate levels specifically.
  2. Private well owners: get tested. If you’re on a private well — more common in eastern Suffolk — you’re responsible for your own testing. The Suffolk County Department of Health Services can guide you on what to test for.
  3. Consider point-of-use filtration. Even if your district treats for PFAS, a reverse osmosis system at the kitchen tap adds another layer of protection. Look for NSF 53 or 58 certification.
  4. Support infrastructure upgrades. Sewer expansion in unsewered areas is one of the most impactful long-term solutions for Long Island’s water quality. It’s expensive and politically contentious, but necessary.

If you’re concerned about your water quality, a certified water treatment professional can test your supply and recommend the right filtration for Long Island’s specific contaminant profile. Given the aquifer’s vulnerability, proactive testing is always a smart investment.

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