PFAS in tap water in the United States

States

The 20 water systems with the highest PFAS-4 values in the United States

Ranked by the sum of the PFAS-4 compounds quantified at the headline sample. Each row links to the system's page with every compound, the sampling history and the source.

The 20 lowest quantified PFAS-4 values in the United States

Only values above the reporting limit are ranked here. In 1,138 systems none of the four compounds was detected above the 3 to 4 ng/L UCMR 5 reporting limits; their pages say what that does and does not mean.

How to read this page

PFAS-4 is the sum of PFOA, PFOS, PFNA and PFHxS, the four PFAS that EFSA judges most harmful. Values are in nanograms per litre (ng/L); 1 ng/L = 0.001 µg/L.

US pages compare against two numbers: 0.5 ng/L for PFAS-4, this site's health benchmark (a documented proposal, not a legal limit, the same on every country's pages), and the 4.0 ng/L federal maximum contaminant level (MCL) for PFOA and for PFOS individually, the US legal limit that applies from April 26, 2029. The EU sum of 20 PFAS is not measured in the United States and never shown on US pages.

Labs count undetected substances as zero, so a PFAS-4 sum is a minimum. A water system only counts as "at or above 0.5 ng/L" when the measurement proves it, and a non-detect only counts as below when the detection limits allow it.

Each system's headline is the newest complete UCMR 5 sample at the entry point with the highest PFAS-4 result, taken where the water enters the distribution system, not at your tap; the system may have changed sources or added treatment since. UCMR 5 reporting limits are 3 to 4 ng/L, so any quantified compound is above the 0.5 ng/L benchmark, and a non-detect reads "below the 3 to 4 ng/L reporting limit", never zero and never "below 0.5 ng/L". EPA's own caveat applies to every value: "UCMR 5 results do not indicate compliance or noncompliance with the PFAS drinking water standards".

How we chose 0.5 ng/L

Legal limits and dates in the United States

The United States has no legal limit for the PFAS-4 sum; this site compares every result with its 0.5 ng/L health benchmark, as on the European pages. EPA's PFAS National Primary Drinking Water Regulation (published April 26, 2024) sets individual maximum contaminant levels (MCLs) of 4.0 ng/L for PFOA and for PFOS, which water systems must meet from April 26, 2029; a PFOA or PFOS result above 4.0 ng/L is marked "above the 2029 federal MCL" on system pages, never as a legal failure, because UCMR 5 results are not compliance data. The same rule set MCLs of 10 ng/L for PFHxS, PFNA and HFPO-DA and a Hazard Index of 1 for their mixture with PFBS; on May 20, 2026 EPA proposed to rescind these four, so pages show them as a secondary line. Enforceable state MCLs in the pilot states: New Jersey: PFNA 13 ng/L, PFOA 14 ng/L, PFOS 13 ng/L; Pennsylvania: PFOA 14 ng/L, PFOS 18 ng/L; Michigan: PFNA 6 ng/L, PFOA 8 ng/L, PFOS 16 ng/L, PFHxS 51 ng/L, HFPO-DA 370 ng/L, PFBS 420 ng/L, PFHxA 400,000 ng/L; Massachusetts: PFAS6 20 ng/L; New York: PFOA 10 ng/L, PFOS 10 ng/L.

Sources, regulators and licences

The U.S. Environmental Protection Agency (EPA) sets the federal drinking-water standards; the state primacy agencies (NJDEP, PA DEP, EGLE, MassDEP, NYSDOH) enforce them and run their own PFAS monitoring. The values on this site come from EPA's Fifth Unregulated Contaminant Monitoring Rule (UCMR 5), a national occurrence survey of PFAS at the entry points of every large and a sample of small public water systems. It is occurrence monitoring, not compliance monitoring: "UCMR 5 results do not indicate compliance or noncompliance with the PFAS drinking water standards". Regulation status as of September 19, 2026.

• U.S. Environmental Protection Agency, Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) occurrence data, final dataset (August 2026) · 1,493 water systems · Licence: Public domain (U.S. federal government work, 17 U.S.C. § 105)

  System registry from EPA SDWIS/ECHO (2026Q2 edition); service areas from EPA ORD (model code MIT); geography from the U.S. Census Bureau. Values are UCMR 5 entry-point results; "UCMR 5 results do not indicate compliance or noncompliance with the PFAS drinking water standards".

Frequently asked questions

Data and downloads

• One JSON file per water system with the headline values, every UCMR 5 sample we hold, the entry points, the PWSID block, the source and the licence: /report/us/{slug}.json (example: /report/us/collegeville-trappe-joint-pwd-pa1460022.json).
• Every system, city and ZIP page of the United States is listed in one sitemap per state: /sitemap-communes-us-nj-0.xml, /sitemap-communes-us-pa-0.xml, /sitemap-communes-us-mi-0.xml, /sitemap-communes-us-ma-0.xml, /sitemap-communes-us-ny-0.xml (/sitemap-index.xml).
• Plain-text summary of the site for AI assistants and crawlers: /llms.txt (full version with the methodology: /llms-full.txt).
• This page and every water system page carry schema.org Dataset markup with the licence, the values, the sample date and the source.