Is PFAS in my tap water dangerous?

Depends on your utility and the levels. At least one PFAS was detectable in about a third of the systems the EPA tested, but most detections are at low nanogram-per-litre levels, and detection is not the same as exceeding a health limit. Check your utility's PFAS results; where levels are elevated, reverse osmosis or a PFAS-certified filter removes them.

How many water systems have PFAS?

In EPA's UCMR 5 monitoring (2023–2025), at least one PFAS was detected in 34.4% of the 10,297 public water systems tested. PFOA and PFOS, the two most-regulated, were each found in roughly 12–13% of systems.

Which PFAS does the EPA regulate in drinking water?

As of the 2024 final rule: PFOA and PFOS at 4 ng/L each, and PFHxS, PFNA and GenX (HFPO-DA) at 10 ng/L each, plus a combined Hazard Index limit for the mixture of PFHxS, PFNA, GenX and PFBS.

Does a Brita filter remove PFAS?

Ordinary carbon pitcher filters are unreliable for PFAS, and short-chain PFAS like PFPeA slip through carbon quickly. Reverse osmosis and filters specifically certified to NSF/ANSI 53 or 58 for PFAS are what reliably reduce them.

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PFAS in US Tap Water

At least one PFAS was detected in 34.4% of the 10,297 U.S. public water systems the EPA monitored under its fifth Unregulated Contaminant Monitoring Rule (UCMR 5, 2023–2025). Detection is not the same as danger — this page pairs the EPA's raw occurrence data with Embr's own verdict and evidence tier for each compound.

Founded by a 19-year firefighter who studies chemical exposure Every claim cited & tiered to the primary literature $0 affiliate — we don't sell filters

What this is

EPA's UCMR 5 required large public water systems — plus a national sample of small ones — to test for 29 PFAS and lithium. This page joins that public dataset to the Embr Bedroom Chemistry Atlas, so every detected compound links to a full, cited page with a plain verdict. Occurrence is not the same as risk: a detection means "measurable," not "unsafe."

The verdicts — the PFAS the EPA now regulates

Five PFAS crossed from monitoring into enforceable federal limits in 2024. Here's our read on each.

Real — regulated, and it lingers

PFOS — one of the two most-detected PFAS

PFOS turned up in about 13% of the water systems the EPA tested — second only to the short-chain acids — and it shares the strictest federal limit, 4 ng/L, set in 2024. It is IARC Group 2B and the PFAS with the deepest human health record.

What matters: check your utility's PFAS results; if elevated, reverse osmosis or a PFAS-certified carbon filter is what actually removes it. In this dataset, 1,309 systems exceeded the limit.

Evidence: Regulatory EPA 4 ng/L · IARC 2B · Peer-reviewed immune & cholesterol effects

Read the full PFOS page

Real — regulated as a mixture

PFHxS — the one that stays longest in you

Found in about 10% of systems. The EPA regulates it two ways — a 10 ng/L individual limit and as one of four PFAS in a combined 'Hazard Index' that caps their joint effect. It has one of the longest human half-lives of any PFAS.

What matters: same fix as the others — reverse osmosis or certified filtration. 171 systems were over the individual limit here.

Evidence: Regulatory EPA 10 ng/L + Hazard Index

Read the full PFHxS page

Real, but uncommon

PFNA — regulated, rarely present

PFNA is regulated (10 ng/L, plus the Hazard Index) but was detected in under 1% of systems — 21 exceeded the limit. Where it shows up it is a genuine concern; for most utilities it simply is not there.

What matters: no action needed unless your utility reports it; if it does, treat it as you would the other PFAS.

Evidence: Regulatory EPA 10 ng/L + Hazard Index

Read the full PFNA page

Real, mostly regional

GenX (HFPO-DA) — the 'replacement' that became a scandal

GenX was the 'safer' PFOA substitute that became its own crisis on North Carolina's Cape Fear River. It is now federally regulated at 10 ng/L. Detected in about 0.5% of systems nationally, but concentrated near its industrial source — a regional problem more than a national one. 16 systems were over the limit.

What matters: mainly relevant downstream of fluoropolymer manufacturing; check your local Consumer Confidence Report if you are in an affected region.

Evidence: Regulatory EPA 10 ng/L + Hazard Index

Read the full GenX page

PFOA — the other 4 ng/L compound — has its own verdict card on the tap-water hub.

Every PFAS the EPA looked for — and what it found

The full UCMR 5 result set, most-detected first. Each compound with an Atlas page links to its full breakdown; the 'verdict' column shows Embr's calibrated read where we have published one.

Contaminant	Detected in	Highest level found	EPA limit (MCL)	Systems over the limit	Embr verdict
Lithium (lithium)	36.44% of 10,299 systems	960 µg/L	—	—	Verdict pending
Perfluoropentanoic acid (PFPeA)	19.75% of 10,289 systems	358 ng/L	—	—	Verdict pending
Perfluorobutanoic acid (PFBA)	18.4% of 10,289 systems	1.7 µg/L	—	—	Verdict pending
Perfluorohexanoic acid (PFHxA)	17.28% of 10,289 systems	260 ng/L	—	—	Verdict pending
Perfluorobutane sulfonic acid (PFBS)	16.27% of 10,289 systems	290 ng/L	—	—	Verdict pending
Perfluorooctane sulfonic acid (PFOS)	12.98% of 10,289 systems	490 ng/L	4 ng/L	1309	Real
Perfluorooctanoic acid (PFOA)	12.52% of 10,289 systems	235 ng/L	4 ng/L	1259	Real
Perfluorohexane sulfonic acid (PFHxS)	9.92% of 10,289 systems	250 ng/L	10 ng/L	171	Real
Perfluoroheptanoic acid (PFHpA)	5.37% of 10,289 systems	72.7 ng/L	—	—	Verdict pending
6:2 fluorotelomer sulfonic acid (6:2 FTS)	1.77% of 10,289 systems	672 ng/L	—	—	Verdict pending
Perfluorononanoic acid (PFNA)	0.81% of 10,289 systems	99.8 ng/L	10 ng/L	21	Real
Hexafluoropropylene oxide dimer acid (GenX) (HFPO-DA)	0.46% of 10,289 systems	140 ng/L	10 ng/L	16	Real
Perfluorodecanoic acid (PFDA)	0.15% of 10,289 systems	12.4 ng/L	—	—	Verdict pending
8:2 fluorotelomer sulfonic acid (8:2 FTS)	0.1% of 10,289 systems	41.9 ng/L	—	—	Verdict pending
4,8-dioxa-3H-perfluorononanoic acid (ADONA) (ADONA)	0.03% of 10,289 systems	8.1 ng/L	—	—	Verdict pending
9-chlorohexadecafluoro-3-oxanonane-1-sulfonic acid (F-53B major) (9Cl-PF3ONS)	0.01% of 10,289 systems	3.4 ng/L	—	—	Verdict pending
11-chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (F-53B minor) (11Cl-PF3OUdS)	0.0% of 10,289 systems	not detected	—	—	Verdict pending

Also monitored, rarely or never found

UCMR 5 tested for these too. Most are obscure short-chain or replacement PFAS detected in a tiny fraction of systems — a few in none at all. We catalogue the notable ones in the Atlas as they warrant.

Perfluoropentane sulfonic acid (PFPeS) — 0.49% of systems
Perfluoroundecanoic acid (PFUnA) — 0.06% of systems
Perfluoroheptane sulfonic acid (PFHpS) — 0.05% of systems
Nonafluoro-3,6-dioxaheptanoic acid (NFDHA) — 0.04% of systems
Perfluorododecanoic acid (PFDoA) — 0.04% of systems
4:2 fluorotelomer sulfonic acid (4:2 FTS) — 0.02% of systems
Perfluoro-3-methoxypropanoic acid (PFMPA) — 0.02% of systems
N-ethyl perfluorooctane sulfonamidoacetic acid (NEtFOSAA) — 0.01% of systems
N-methyl perfluorooctane sulfonamidoacetic acid (NMeFOSAA) — 0.01% of systems
Perfluoro-4-methoxybutanoic acid (PFMBA) — 0.01% of systems
Perfluoro(2-ethoxyethane)sulfonic acid (PFEESA) — not detected in any system
Perfluorotetradecanoic acid (PFTA) — not detected in any system
Perfluorotridecanoic acid (PFTrDA) — not detected in any system

How to read this — the honest caveats

Occurrence is not risk. A detection means the compound was measurable at or above the lab reporting level — not that any given home's water is unsafe.
The systems here are those required to monitor under UCMR 5 (generally larger public water systems plus a national sample of small ones). Private wells are not covered — if you are on a well, no one tests this for you.
Detection frequency depends on the analytical reporting level; a "non-detect" means "below the reporting level," not necessarily zero.
The EPA limits shown are the final 2024 values for the individually-regulated PFAS. PFHxS, PFNA and GenX are also regulated together through a Hazard Index, which this table does not compute.
Embr's verdicts are our own calibrated judgment layer; only compounds we have reviewed carry one. "Verdict pending" means not-yet-reviewed, not "safe."

Sources

EPA, Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) occurrence data, 2023–2025 — the source of every occurrence figure on this page. epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule — Regulatory
EPA, PFAS National Primary Drinking Water Regulation (final rule, April 2024) — the enforceable MCLs and Hazard Index. epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas — Regulatory
Embr Bedroom Chemistry Atlas — the compound pages and the calibrated verdicts this data is joined to. embrsleep.com/atlas — Industry (self/first-party)

For the rest of what's in your tap water, see the tap-water hub — lead, arsenic, disinfection byproducts and more. And if you're deciding what to do about it, which filter actually removes PFAS — most pitchers don't.

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