PFOA and PFOS limits explained

EPA's limits for PFOA and PFOS in public drinking water are 4.0 parts per trillion (ppt) each, and on 16 October 2026 both are still in force. Water systems have until April 26, 2029 to meet them. EPA has proposed letting systems ask for two more years, to April 26, 2031, but that proposal is not final.

What the limit means

One ppt is one nanogram per liter. In EPA's April 2024 rule, the health goal (MCLG) for PFOA and PFOS is zero and the enforceable limit (MCL) is 4.0 ppt. The regulation, 40 CFR 141.61(c), writes it as 0.0000040 milligrams per liter.

Compliance is judged on a running annual average at each sampling point (EPA). One sample above 4.0 ppt is usually not a violation by itself. The exception is a single result so high that later samples could not bring the average back under the limit, for example one more than four times the limit. Then the system is out of compliance at once (40 CFR 141.903(e)).

EPA's standard health statement for water reports says that drinking water above the PFOA or PFOS limit for many years may raise the risk of cardiovascular, immune and liver effects and of certain cancers. It adds that repeated exposure during pregnancy or childhood may raise the risk of developmental and immune effects (EPA).

All six PFAS limits on 16 October 2026

Limits and goals are from EPA and 40 CFR 141.61(c).

On May 20, 2026, EPA published two proposals. One would rescind the limits for PFHxS, PFNA, HFPO-DA and the Hazard Index. The other would let systems that ask move the PFOA and PFOS deadline from April 26, 2029 to April 26, 2031. Comments on both closed July 20, 2026. Neither is final, so all six limits are still in the regulation.

The Hazard Index adds up four ratios: each PFAS level divided by its health-based number, which is 10 ppt for PFHxS, PFNA and HFPO-DA and 2,000 ppt for PFBS. A total above 1 exceeds the limit (40 CFR 141.61(c)).

Deadlines

• 2027: systems finish initial PFAS monitoring and start telling customers their levels (EPA).
• 2029: systems must meet the limits (EPA). For PFOA and PFOS the date is April 26, 2029 (Federal Register). If the extension becomes final, systems that ask would have until April 26, 2031.

What UCMR 5 found

EPA's UCMR 5 survey sampled public water systems from 2023 to 2025. Among large systems (more than 10,000 people) with a full set of results, 12.2% had at least one sampling location whose average was above 4.0 ppt for PFOS, and 11.0% for PFOA (EPA UCMR 5 Data Summary, July 2026). For each of the four limits proposed for rescission, the share was 1.1% or less (same source).

Of the 50 largest US water systems, 49 have UCMR 5 results. Using EPA's comparison method, 12 of them had at least one sampling location whose average was above the PFOA or PFOS limit (how we counted). See which 12 systems, with the data to download.

EPA states that UCMR 5 results do not show compliance or noncompliance with the limits (EPA). They are a screening snapshot. Compliance monitoring is a separate step.

What to do with your utility's numbers

1. Find your utility's PFOA and PFOS results. EPA suggests asking your water provider first (EPA fact sheet). Your water quality report may list them too; see how to read your water quality report.
2. If PFAS were not measured, or were measured below the federal limits, EPA says a filter may not be useful to you (same source).
3. If you want a filter, EPA says to look for certification to NSF/ANSI 53 or NSF/ANSI 58 for PFAS reduction. EPA's fact sheet adds that, as of April 2024, those certifications focused on PFOA and PFOS and did not yet show reduction down to EPA's new limits (same source). Some listings now also carry a "Total PFAS" claim, for example the IAPMO listing for the PUR PLUS faucet filter (IAPMO W-29904).
4. Check that the listing names your exact model and cartridge, and replace the cartridge on schedule. EPA says a filter only works if it is maintained (same source).

You can search listings at IAPMO R&T, NSF and WQA.