PFAS in Drinking Water: The 2024 EPA Limits and Which Filters Are Certified to Remove Them

What PFAS, PFOA, and PFOS are

PFAS stands for per- and polyfluoroalkyl substances, a large family of synthetic chemicals used since the mid-twentieth century in products like nonstick coatings, stain and water repellents, and firefighting foam. Their carbon-fluorine bonds are very stable, which is why they are often called 'forever chemicals': they break down slowly and can persist in water and soil.

PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) are two of the most studied individual PFAS. They are the two compounds the EPA regulated most strictly in drinking water, which is why filter standards and certifications tend to single them out by name.

The EPA's 2024 drinking-water limits

On April 10, 2024, the EPA finalized a National Primary Drinking Water Regulation for six PFAS, with the rule effective June 25, 2024. It set enforceable Maximum Contaminant Levels (MCLs) of 4.0 parts per trillion (ppt) each for PFOA and PFOS. A part per trillion is roughly one drop in an Olympic-sized pool, which gives a sense of how low these limits are.

The same rule set individual MCLs of 10 ppt for three other PFAS (PFHxS, PFNA, and HFPO-DA, the last commonly called GenX chemicals), plus a Hazard Index of 1 for mixtures of those and PFBS. These limits apply to public water systems, the utilities that supply most homes.

The rule includes a compliance timeline. Public water systems were given time to complete initial monitoring and reporting, and additional years to bring water into compliance with the MCLs where exceedances are found. The EPA has also proposed adjustments to the compliance schedule, so the exact dates a given utility must meet can shift; the 4 ppt limits for PFOA and PFOS are the anchor figures to remember.

How to find out if your water has PFAS

If you are on a public water system, start with your annual Consumer Confidence Report (CCR). Utilities serving more than 25 people must publish one each year, and it lists detected contaminants. Search for your utility's name plus 'consumer confidence report,' or use the EPA's CCR resources to locate it. As PFAS monitoring data from the 2024 rule comes in, results increasingly appear in these reports and in state databases.

The EPA's PFAS Analytic Tools, part of the ECHO system, pull national datasets into a searchable map that includes drinking-water testing results and facilities that may use PFAS. It is a useful way to see what has been measured in your area, though coverage varies by location and reporting year.

If you are on a private well, no utility tests it for you. PFAS are not detectable by taste, smell, or color, so the only way to know is laboratory testing. Use a certified laboratory and follow its sampling instructions closely, because PFAS testing is sensitive to contamination from common household materials during collection.

Which filter certifications actually address PFAS

Not every filter reduces PFAS, and a general claim is not enough. Look for certification to a standard that names PFOA and PFOS. NSF originally created a dedicated protocol, NSF P473, for PFOA and PFOS reduction. In 2017 the NSF Joint Committee folded those requirements into NSF/ANSI 53 (for activated carbon and anion-exchange systems) and NSF/ANSI 58 (for reverse osmosis systems).

In practice that means three certification paths are worth looking for: a filter certified to NSF/ANSI 53 with a specific PFOA/PFOS reduction claim, a filter still referencing the older P473 protocol, or a reverse osmosis system certified to NSF/ANSI 58 for PFOA/PFOS. Reverse osmosis is generally effective against a broad range of PFAS because it filters at the membrane level rather than relying on adsorption alone.

One caveat on the numbers: the acceptance level historically built into these PFOA/PFOS certifications was tied to an older EPA health advisory and is higher than the 4 ppt MCL the EPA set in 2024. A certification confirms the filter reduces PFOA and PFOS to the level the standard specifies; it does not automatically prove performance down to 4 ppt. Read the certified claim for what it states rather than assuming it matches the latest regulation.

How to verify a PFAS filter claim

Treat a PFAS claim like any other certification claim. Look up the exact model in a certifier's public database: NSF at info.nsf.org/Certified/DWTU, WQA at find.wqa.org/find-products, or IAPMO R&T at pld.iapmo.org. Confirm that the listing names PFOA and PFOS specifically, not just 'contaminant reduction' in general.

Be skeptical of 'tested to' language on PFAS products. A page that says a filter was 'tested to reduce PFOA and PFOS' but whose model does not appear in any certifier database is giving you the manufacturer's own result, not a verified certification. For a contaminant measured in parts per trillion, the difference between an audited certification and a one-time lab test is worth caring about.

Maintenance is part of performance

A certified PFAS filter only performs as certified if you replace the cartridge or membrane on schedule. Reduction certifications are tied to a rated capacity, the volume of water the media is verified to treat. Past that point, performance is no longer covered by the certification.

Follow the manufacturer's replacement interval, and if your water has tested high for PFAS, consider replacing media more conservatively rather than waiting for the maximum rated volume. The filter is a system you maintain, not a one-time purchase.