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PFAS 'Forever Chemicals' in U.S. Tap Water

EPA's UCMR5 program found PFOA or PFOS above the 2024 federal limit of 4 parts per trillion in 1,721 public water systems — serving about 81 million people.

What this means, in plain English

PFAS are man-made chemicals used in things like nonstick pans, grease-proof food wrappers, and firefighting foam. People call them “forever chemicals” because they barely break down — not in nature, and not in your body, where they can build up over years. Scientists have linked them to certain cancers, thyroid problems, high cholesterol, and harm to a baby’s development. In 2024 the EPA set the first-ever nationwide limit: no more than 4 parts per trillion of the two most-studied kinds, PFOA and PFOS. When the EPA actually tested public water systems, 1,721 came back over that limit — and together those systems serve about 81 million people.

💧 How small is 4 parts per trillion? One part per trillion is roughly a single drop of water in 20 Olympic-sized swimming pools. PFAS can be harmful at astonishingly tiny amounts, which is why the limit is set so low.

What you can do

Look up your own water system to see whether PFAS was found. If it was, a reverse-osmosis system — or a filter independently certified to the NSF/ANSI 53 standard for PFAS — will reduce it at your tap. A basic taste-and-odor filter will not.

By state

States ranked by number of affected public water systems. Click a state for its city-by-city water quality.

Most affected water systems

The 250 highest-ranking systems. Search for your city or utility.

No matches.

Terms, explained

PFAS

A big family of man-made “forever chemicals” (per- and polyfluoroalkyl substances). They resist heat, water, and grease, so they’re used in nonstick and waterproof products — and they don’t break down.

PFOA and PFOS

The two most common and most-studied PFAS chemicals. They’re the ones the EPA’s 2024 limit covers.

Parts per trillion (ppt)

A way to measure very tiny amounts. One part per trillion is about one drop of water in 20 Olympic swimming pools. The limit for PFOA and PFOS is 4 ppt.

UCMR5

The EPA program (the fifth “Unregulated Contaminant Monitoring Rule”) that required water systems to test for PFAS from 2023 to 2025. It’s where this data comes from.

Methodology & sources

EPA UCMR5 (Fifth Unregulated Contaminant Monitoring Rule, 2023–2025 sampling). PFAS limit per the 2024 EPA PFAS National Primary Drinking Water Regulation (4 ppt for PFOA and PFOS).

Important caveat: UCMR5 monitors all systems serving >3,300 people plus a national sample of smaller ones. A system with no PFAS shown here may simply not have been sampled — absence of data is not proof of safety.

This study draws on 21,807 U.S. public water systems and our full certified-filter database. All EPA data is public domain.