What PFAS are, in one paragraph
PFAS (per- and polyfluoroalkyl substances) are synthetic chemicals used since the 1940s in non-stick, stain- and water-repellent products and firefighting foam. They barely break down, which is why they are called 'forever chemicals,' and they accumulate in water and in the body over time.
The 2024 rule, in plain numbers
EPA's 2024 drinking-water rule set maximum contaminant levels of 4.0 ng/L for PFOA and for PFOS, and 10 ng/L for PFHxS, PFNA and HFPO-DA (GenX). In May 2026 EPA proposed keeping the PFOA and PFOS limits, with the option of until 2031 to comply, and rescinding the other three. Until a final rule, all five limits apply.
The 2024 rule also set a Hazard Index of 1 for mixtures of two or more of PFHxS, PFNA, GenX and PFBS; EPA has proposed rescinding it, and it applies until a final rule.
Compliance with the 2024 limits is judged on a running annual average, with a compliance date of 2029 (EPA has proposed allowing until 2031 for PFOA and PFOS).
A nanogram per litre (ng/L) is one part per trillion. The limits sit this low because these compounds accumulate and, for PFOA and PFOS, the health goal is zero.
Why the limits are near zero
For most contaminants a limit balances risk against treatment cost. For PFOA and PFOS the health goal (MCLG) is zero: studies link them to immune, liver, thyroid and developmental effects and to certain cancers, and because they build up over time the EPA does not identify a threshold with no risk. The enforceable number is then set at the edge of what testing can detect.
How to check your own water
PurityMap reads the EPA UCMR5 monitoring record for thousands of US systems. Use the PFAS checker or your city water report to see whether PFOA, PFOS or PFHxS were measured where you live, the exact value, and how it compares to the federal limit. As a worked example, Tucson Water's EPA record shows PFOA and PFOS not detected, below 4 ng/L — a non-detect reflects the test's reporting limit, not a guarantee of zero.
EPA's 2024 limits are judged on a yearly average, and water systems have until 2029 to meet them, so a single sample is not a violation.
What to do if PFAS is detected in your water
Take these steps in order. Start with the exact result, not the headline. PurityMap may earn an affiliate commission on some product links, at no cost to you.
- Read the exact result
Note which compound was found, the amount in ng/L, the sample date, and whether it is one sample or a yearly average. Our water test results reader compares a number you type with its federal reference.
- Ask your water utility
Ask for its latest PFAS results and what it plans to do. Your state environmental agency or health department may also have results and recommendations for your area.
- Decide whether a filter fits
EPA says a filter may not be useful if PFAS have not been measured in your water, or were measured below federal limits. No result can mean it wasn't tested, so ask your utility, or test a private well. If your result is above a limit, a certified home filter is one way to reduce your exposure.
- Choose a certified filter
EPA lists activated carbon (GAC), ion exchange and reverse osmosis as home options. Look for NSF/ANSI 53 or 58 with the compound in your result named in the listing, not a generic purifier claim, then check the model in the certifier's directory.
- Keep it working
Replace cartridges on the manufacturer's schedule. EPA warns that a filter past that schedule can increase your risk of exposure. Re-test to confirm it is working.
Boiling water does not remove PFAS. Sampling reported by the Minnesota Department of Health found whole-house softeners and iron filters do not remove it either.
EPA's home-filter guidance, as of April 2024, says certifications focus on PFOA and PFOS and do not yet show a filter reaches EPA's 2024 limits, though reducing PFAS still limits your exposure. Some listings show a combined Total PFAS claim, which doesn't establish any one compound, so check that the listing names the compound in your result. A listing may not cover PFHxS, PFNA or GenX.
EPA's rule covers public water systems, not private wells. A certified laboratory test is the way to know what is in yours.
This article summarizes the 2024 federal PFAS rule and general information about these compounds. It is not medical advice and does not determine whether any water is fit for a specific person. For concerns about PFAS exposure — especially during pregnancy or for children — consult a licensed healthcare professional, and use a certified laboratory to test your own water.