Contaminant Guide

PFAS in Well Water

PFAS (per- and polyfluoroalkyl substances) are a large family of synthetic chemicals used in firefighting foam, non-stick coatings, and industrial processes. They persist indefinitely in the environment — earning the name "forever chemicals." In 2024 the EPA set the first-ever federal MCL for PFAS at 4 parts per trillion, with an MCLG of zero, reflecting that no safe level has been established.

What are PFAS?

PFAS (per- and polyfluoroalkyl substances) encompass thousands of synthetic chemicals sharing an extremely stable carbon-fluorine bond. The most studied — PFOA and PFOS — have been phased out of U.S. production but remain widespread in the environment due to their persistence. Replacement PFAS (short-chain variants) are now also detected in groundwater.

PFAS cannot be seen, smelled, or tasted in water. There is no way to detect them without laboratory analysis.

Sources in groundwater

The highest-risk sources near private wells:

  • AFFF (aqueous film-forming foam) — used at military bases, airports, and fire training sites; the largest single source of PFAS groundwater contamination in the U.S.
  • Industrial facilities — chemical plants, electronics manufacturers, chrome plating operations
  • Landfills — PFAS-containing consumer products leach into leachate
  • Biosolids (sewage sludge) — applied to agricultural fields; a diffuse but widespread source

How common is PFAS in well water?

PFAS contamination is most documented in Michigan, New Hampshire, Massachusetts, North Carolina, and Alabama — states with high military base density or industrial history. However, national USGS surveys find PFAS detectable in roughly 45% of U.S. drinking water sources tested, with private wells near contamination sources at highest risk. Michigan has one of the most extensive PFAS groundwater contamination records in the country.

Health effects

  • Kidney cancer (PFOA) — IARC classifies PFOA as a Group 1 carcinogen (sufficient evidence in humans); elevated risk documented in occupationally exposed workers and communities near manufacturing plants.
  • Thyroid disruption — PFAS interfere with thyroid hormone production and transport; associated with hypothyroidism and altered TSH levels in epidemiological studies.
  • Immune suppression — Reduced vaccine antibody response in children is one of the most consistent PFAS health findings; the immune effects drove EPA's 2024 MCL rulemaking.

The EPA limit: MCL = 4 ppt, MCLG = 0

In April 2024, EPA finalized MCLs for six PFAS compounds — the first federal drinking water standards for PFAS. PFOA and PFOS each have an MCL of 4 ppt (0.004 µg/L). The MCLG for both is zero — meaning EPA acknowledges no safe level exists. PFNA, PFHxS, and HFPO-DA have individual MCLs; mixtures are regulated by a hazard index.

These MCLs apply to public water systems. Private wells have no federal testing requirement, but the health basis for the MCLs applies equally to well water.

Testing

PFAS testing requires a certified laboratory with LC-MS/MS capability (EPA Method 533 or 537.1). Standard lab panels test 18–40 PFAS compounds. Costs typically run $150–400 depending on panel size. If you are near a military base, airport, or industrial site, test for PFAS specifically — standard well water panels do not include it.

Find a certified PFAS lab and learn how to collect a sample

Treatment

  • Reverse osmosis (RO) — most effective, removes >95% of PFAS across all chain lengths including short-chain variants. Best choice for point-of-use.
  • Granular activated carbon (GAC) — effective for long-chain PFAS (C8+); less effective for short-chain PFAS (PFBS, PFBA) and next-generation replacements. Common in whole-house systems.
  • Anion exchange resin (PFAS-selective) — single-use ion exchange resins can achieve very high removal; gaining traction for whole-house treatment.
  • Nanofiltration — membrane technology effective for PFAS; less common in residential applications.

Compare PFAS treatment systems for private wells

PFAS in municipal water supplies

Municipal water systems are regulated under the Safe Drinking Water Act (SDWA) and must now comply with the 2024 EPA PFAS MCLs. Systems serving 25 or more people must test for PFAS and report results in annual Consumer Confidence Reports (CCRs).

If your utility serves an area with known PFAS contamination, your CCR will show whether levels exceed the new MCLs and what treatment actions are being taken. Many utilities are installing GAC or reverse osmosis at the treatment plant level.

If you are on municipal water and concerned about PFAS, read your most recent CCR, available from your utility or at the EPA's online database. If you want additional assurance, a point-of-use RO filter at your tap provides an extra treatment barrier.

Learn how to read a Consumer Confidence Report

Regulatory framework

MCL (PFOA): 4 ppt (0.004 µg/L). MCLG: 0.
MCL (PFOS): 4 ppt. MCLG: 0.
PFNA, PFHxS, HFPO-DA: individual MCLs. Mixtures regulated by hazard index.
Rule: National Primary Drinking Water Regulation for PFAS, EPA, April 2024. Compliance deadline: 2027 for most systems.

MCLG=0 for PFOA and PFOS reflects carcinogenicity classification with no established safe threshold. This mirrors the arsenic regulatory structure — feasibility-based MCL set above a zero MCLG.

Detection

EPA Method 533 (developed 2019) and Method 537.1: liquid chromatography tandem mass spectrometry (LC-MS/MS). Method 533 covers a broader range of short-chain PFAS. Detection limits are sub-ppt. Standard ICP-MS does not detect PFAS. Specialized certified labs required; sample collection protocol is critical to prevent contamination from PTFE sampling equipment.

Chemistry and persistence

The C-F bond is among the strongest in organic chemistry, making PFAS essentially non-biodegradable under environmental conditions. PFOA and PFOS are fully fluorinated carboxylic and sulfonic acids respectively. They are highly water-soluble, mobile in groundwater, and bioaccumulative. Half-lives in human serum are measured in years (PFOA ~3.5 years, PFOS ~5.4 years).

Data access

EPA's UCMR 5 survey (2023–2025) generates the first nationally representative PFAS occurrence data for public systems. ATSDR's PFAS exposure data and state environmental agency records document groundwater plumes near contaminated sites.

Access our data API and methodology

References

  1. Hu, X.C., Andrews, D.Q., Lindstrom, A.B., et al. (2016). Detection of poly- and perfluoroalkyl substances (PFASs) in U.S. drinking water linked to industrial sites, military fire training areas, and wastewater treatment plants. Environmental Science & Technology Letters, 3(10), 344-350. https://doi.org/10.1021/acs.estlett.6b00260
  2. Grandjean, P., Heilmann, C., Weihe, P., et al. (2017). Estimated exposures to perfluorinated compounds in infancy predict attenuated vaccine antibody concentrations at age 5-years. Journal of Immunology Research, 2017. https://doi.org/10.1155/2017/6462138
  3. Steenland, K., Fletcher, T., & Savitz, D.A. (2010). Epidemiologic evidence on the health effects of perfluorooctanoic acid (PFOA). Environmental Health Perspectives, 118(8), 1100-1108. https://doi.org/10.1289/ehp.0901827