The numbers, and who they bind

EPA set enforceable Maximum Contaminant Levels for six PFAS.

Compound MCLG (health goal) MCL (enforceable)
PFOA Zero 4.0 ppt
PFOS Zero 4.0 ppt
PFHxS 10 ppt 10 ppt
PFNA 10 ppt 10 ppt
HFPO-DA (GenX) 10 ppt 10 ppt
Mixtures of 2+ of PFHxS, PFNA, HFPO-DA, PFBS Hazard Index 1 Hazard Index 1

Update: four of the six are proposed for rescission

On 18 May 2026 EPA announced two proposed rules. One would uphold the regulation for PFOA and PFOS, while letting systems request two more years — to 2031 — to comply. The other would rescind the regulations for PFHxS, PFNA, HFPO-DA (GenX) and the Hazard Index mixture of those three plus PFBS.

Both are proposals open for public comment. The April 2024 rule covering all six stands until a final rule changes it, so the table above is still the law today.

What it changes for a household is narrow. The two compounds with the lowest limits, and the only two with named NSF reduction claims, are the two the proposal keeps.

→ Unregulated contaminants, and how a limit is set or removed

Two things in that table are routinely misread.

The MCLG for PFOA and PFOS is zero. That is the health-based goal, and EPA set it at zero because no level is identified as safe. 4.0 ppt is the enforceable level — the point at which a utility must act. It is not a threshold below which the water is established as safe.

The mixture limit is separate. Water can pass every individual MCL and still fail the Hazard Index, because that limit accounts for combined and co-occurring levels. A single-compound result does not establish compliance.

These limits bind public water systems. Private wells sit outside the rule entirely, exactly as with nitrate and arsenic.

Why your water report probably says nothing

Public water systems have three years to complete initial monitoring — by 2027 — and must inform the public of PFAS levels beginning that same year.

So until 2027, many utilities hold no PFAS data at all. An absent figure in a Consumer Confidence Report reflects an absent test, not an absent contaminant.

Then the deadline that matters: systems have until 2029 to reduce PFAS where monitoring shows levels above the MCLs, and only from 2029 must they notify the public of a violation.

Read plainly, that means a utility can lawfully deliver water above the PFAS limits for years yet, without being in violation and without telling you. Compliance is also measured on running annual averages at the sampling point, so one high result is not itself a violation.

The sentence the filtration industry does not repeat

This is the fact that should govern the purchase, and EPA states it directly:

It’s important to note that the current certification standards for PFAS filters (as of April 2024) do not yet indicate that a filter will remove PFAS down to the levels EPA has now set for a drinking water standard. EPA is working with standard-setting bodies to update their filter certifications to match EPA’s new standards.

A filter certified for PFAS reduction was tested against the reduction targets that existed when the standard was written. Those targets predate the 4.0 ppt MCL. So “NSF/ANSI 53 certified for PFAS reduction” is evidence the product does something measurable — and is not evidence it reaches the enforceable limit.

It does not mean certified filters fail. It means the certification answers a different question from the one the new rule asks, and EPA says it is working to close that gap.

And certification is per compound

PFAS is a family of thousands of compounds. Certification is granted per claim, which is the same rule that governs every NSF standard: under NSF/ANSI 58, TDS reduction is the only required claim, and everything else is optional.

EPA’s own instruction is to “check NSF website to see if product treats the type of PFAS you’re trying to remove.” A filter certified for PFOA and PFOS establishes nothing about PFHxS, PFNA, GenX or PFBS — including the four compounds that carry the mixture limit.

What EPA says actually works

For water systems, EPA identified four Best Available Technologies: granular activated carbon, anion exchange, reverse osmosis, and nanofiltration.

Note what BAT designation means. EPA weighs removal efficiency alongside full-scale operating history, geographic applicability, compatibility with other processes, and reasonable cost to medium and large systems. It is not a ranking of removal performance, and EPA states systems are not limited to the BATs.

One exclusion is worth carrying into a shop. EPA declined to designate powdered activated carbon, because “its efficacy for PFAS removal is variable due to factors such as carbon particle size, background organics, and plant efficiency.” Granular activated carbon is a BAT; powdered is not. A product label reading only “activated carbon” has not told you which you have.

For homes, EPA found the granular activated carbon, ion exchange and reverse osmosis point-of-use systems it studied “can greatly reduce PFAS levels” — with the condition that “filters are only effective if they are maintained according to the manufacturer’s instructions.”

“Greatly reduce” is EPA’s wording. It is not a percentage, and we are not going to invent one.

Choose a point-of-use system if

  • You are on a public water system and your utility has published a PFAS result at or above an MCL, or has published nothing and you want to act before 2029.
  • You want drinking and cooking water treated. PFAS is a long-term ingestion concern, so treating a single tap covers the exposure route that matters.
  • The model names the specific PFAS compounds it is certified to reduce, and those include the ones in your result.
  • You will actually replace the media on schedule. EPA makes maintenance a condition of effectiveness, not a footnote.

Choose to test first if

  • Your utility has not yet published PFAS data, which before 2027 is most of them.
  • You are on a private well. The rule does not reach you and no one is sampling.
  • A supplier has quoted you a PFAS removal percentage. Ask which compounds, at what influent concentration, and against which standard — EPA publishes no such figure for home filters.

Choose to do nothing yet if

  • You have a published result well below the MCLs across all six limits, including the Hazard Index for the mixture.
  • Your only evidence is a regional map or a neighbour’s result. PFAS contamination is source-specific and does not transfer down the street.

Mistakes that cost the most money

Reading a certification badge as compliance. EPA says current PFAS filter certification does not yet demonstrate reduction to the MCL. The badge and the limit answer different questions.

Reading a silent water report as a clean one. Before 2027 most utilities hold no PFAS data. Nothing published means nothing measured.

Assuming “meets standards” means below the MCL. Systems have until 2029. A utility can be fully compliant today and still deliver water above 4.0 ppt.

Buying whole-house for an ingestion problem. PFAS exposure through drinking and cooking is what the limits address. Treating every tap costs more and treats water you do not swallow.

Confusing powdered with granular carbon. EPA designated granular activated carbon a Best Available Technology and explicitly declined powdered. A label reading “activated carbon” has not said which.

Skipping media replacement. EPA makes maintenance a condition of effectiveness. An exhausted filter is not a slower filter, it is a bypass.

Treating a neighbour’s result as yours. PFAS contamination is source specific. It tracks industrial sites, airfields and fire-training grounds, not postcodes.

Three situations, and what changes

Your utility published a result at or above an MCL. Act on the compound named. Match a point-of-use system certified for that specific PFAS, and ask what the certification demonstrates about your result rather than about the category.

Your utility has published nothing. This is most of them before 2027. You are deciding under absent data, so the choice is between testing privately and treating pre-emptively at one tap. Both are defensible; guessing is not.

You are on a private well. The rule does not reach you. No monitoring deadline applies, no notification will arrive, and nobody samples your water. A certified lab test is the only route to a number.

The objections worth answering

“My utility says the water meets all standards.” Both can be true. The compliance deadline is 2029, and until then a system above the PFAS MCLs is not in violation. Compliance is also measured on running annual averages, so a single high sample does not breach the standard.

“Isn’t a filter pitcher enough?” Possibly, for the compounds it is certified against. EPA found point-of-use granular carbon, ion exchange and reverse osmosis can greatly reduce PFAS. It also says certification does not yet demonstrate reaching the MCL, so ask which compounds and what the test showed.

“PFAS is in everything, so why treat water at all?” Because water is the exposure route EPA has now set enforceable limits on, and the one you can control at a single tap for a known cost.

Who this is for

Households on a public water system deciding whether to treat before the 2029 compliance deadline, and private-well owners who fall outside the rule entirely. It assumes you want a cited number rather than reassurance.

What to ask before buying

Which PFAS compounds is this model certified to reduce, under which standard, and what does the certification demonstrate about reaching 4.0 parts per trillion?

If the answer is a logo and the word “PFAS”, you have learned something. EPA’s listing, not the box, is where that question gets answered.

→ What each NSF standard covers, and the one required claim → The full treatment sequence and where point-of-use sits → Why your water report may say nothing about PFAS → City water treatment: what your utility handles, and what it does not → Every filter NSF lists for PFAS reduction, and the three separate claims → EPA names four technologies for every regulated PFAS