What this ranking counts
In 2024 the U.S. EPA set the first enforceable national limits for several PFAS (the “forever chemicals”) in public drinking water. Two of them, PFOA and PFOS, now carry a maximum contaminant level (MCL) of 4.0 nanograms per litre (ng/L) each. Around the same time, every large public water system reported PFAS results under the federal UCMR5 monitoring program. Reading those results against the new limits, PurityMap counted the cities where an EPA sample came back above them.
This is a ranking of what public monitoring records show, not a health scoreboard. A city appears here because one EPA sample measured above a limit EPA set in 2024, which is a specific, checkable fact, and a different thing from a statement about anyone’s health. That limit is judged on a yearly average, and water systems have until 2029 to meet it, so a single sample is not a violation. 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).
What the records find
Across the systems in PurityMap’s dataset, PFOS had a sample above a 2024 EPA limit in 746 monitored cities, PFOA in 728, and PFHxS in 86. The limits are 4.0 ng/L for PFOA and for PFOS, and 10 ng/L for PFHxS, PFNA and GenX. EPA has proposed rescinding the PFHxS, PFNA, GenX and Hazard Index limits; they apply until a final rule. The highest monitored PFOS results include Emmaus, Pennsylvania at 153 ng/L, Grand Prairie, Texas at 82 ng/L, Oxford, Mississippi at 72.2 ng/L, and Irondale, Alabama at 59.4 ng/L. Each figure is the highest result reported for that system in the 2024 UCMR5 round.
The full ranking lists the highest monitored PFOS results city by city, each row linking to that city’s water report and its underlying source. You can see the complete list on the ranking of U.S. cities with a PFAS sample above a 2024 EPA limit.
MCL (maximum contaminant level): the highest concentration of a contaminant allowed in public drinking water under federal rules. It is a regulatory limit, set with treatment feasibility in mind. It is not a line above which harm begins and below which it stops.
How strong the evidence is
These numbers come from EPA UCMR5, the fifth Unregulated Contaminant Monitoring Rule, which required standardized PFAS sampling at public water systems and released occurrence data in early 2026. That makes the dataset unusually consistent: the same analytes, methods and reporting limits across the country.
Two limits are worth keeping in mind. First, these are results for monitored public-system water during a defined period, not necessarily the water leaving your tap today, and not the raw source water, which a utility may treat before delivery. Second, monitoring covered systems above a size threshold, so the absence of a city from this list is not proof of absence; it can also mean the system was not in this monitoring round.
What it means at home
A public-system record describes the water a utility delivered to its distribution network. Your own tap can differ: older household plumbing, building-specific fixtures and the exact point you draw from all matter. The way to connect this ranking to your home is to start from your own supplier: confirm which system serves your address on your utility bill, then read that system’s PFAS finding and the dated source behind it.
If your city is on this list, the record is telling you one EPA sample was above a 2024 limit for that period. That limit is judged on a yearly average, and water systems have until 2029 to meet it, so a single sample is not a violation. 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). What you do with that is a personal decision, and for a definitive answer about your specific tap, a certified home test is the only way to measure it directly.
What to do next
Three steps follow naturally. Confirm your serving system and open its water report to see the exact PFAS numbers and their sources. Read the PFAS explainer for what the compounds are, where they come from and which treatment methods reduce them. And if you decide to treat water at the tap, look for filters independently certified to reduce PFOA and PFOS. Reverse osmosis and certain activated-carbon systems are the common options, and the certification should name the exact model.
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.
PurityMap’s filter guidance is evidence-based, not paid placement. Some product links are affiliate links, and PurityMap may earn a commission from qualifying purchases at no extra cost to you; that never changes which products the records support.
This article is general information, not medical advice. Public-system monitoring records are not a measurement of the water at your specific tap. For decisions about your health or your household’s water, consult a qualified professional and test your own water.