PFAS in Drinking Water: The 2024 EPA Rule, MCLs, and Filtration Options

What PFAS are

Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic chemicals containing carbon-fluorine bonds; EPA's fifth Unregulated Contaminant Monitoring Rule sampled drinking water for 29 of them. The carbon-fluorine bond is one of the strongest in organic chemistry, making PFAS exceptionally persistent in the environment. They do not biodegrade meaningfully on human timescales, which is why they are commonly called "forever chemicals".

PFAS have been used since the 1940s in non-stick cookware coatings (Teflon and similar), water-repellent textiles, stain-resistant carpet and upholstery, food-packaging coatings, and aqueous film-forming foam (AFFF) used in firefighting. Industrial discharge, AFFF deployment at military and civilian airfields, landfill leachate, and consumer-product disposal have introduced PFAS into surface and groundwater across the U.S.

How widespread it is, per EPA's own monitoring

EPA released the final dataset from its fifth Unregulated Contaminant Monitoring Rule (UCMR 5) in August 2026. The accompanying UCMR 5 Data Summary (EPA 815-S-26-007, July 2026) covers roughly 10,130 public water systems across about 25,950 sampling locations, and is the most complete national picture available. Its headline findings:

• 7.8 percent of public water systems nationwide (EPA's weighted estimate) had one or more running annual average above a PFAS MCL from the 2024 rule.
• That rate climbs with system size: 7.1 percent of systems serving fewer than 3,300 people, 8.3 percent serving 3,300 to 10,000, and 15.5 percent serving more than 10,000.
• PFAS arrive as mixtures, not singly. 66 percent of sampling locations with at least one PFAS detected at or above the reporting limit had multiple PFAS at or above it.

EPA is explicit that UCMR 5 results “do not indicate compliance or noncompliance with the MCLs” - compliance is determined from quarterly running annual averages reported to the state primacy agency. Read these as occurrence data, not as a violation list. The co-occurrence finding is the one with the clearest household implication: a filter certified only for PFOA and PFOS addresses two of the compounds likely present, which is the argument for the broader Total PFAS Reduction claim.

The 2024 EPA final rule

EPA's final PFAS NPDWR was published in the Federal Register on April 26, 2024. The rule establishes enforceable Maximum Contaminant Levels for six PFAS compounds:

For context, 4 ng/L is approximately 4 parts per trillion. This is among the lowest enforceable drinking water concentrations EPA has ever set for any contaminant. Analytical methods that can reliably detect PFAS at this level were not commercially available a decade ago.

Public water systems have until 2027 to complete initial monitoring and 2029 to achieve compliance with the MCLs. EPA's May 18, 2026 proposed compliance-extension rule would push the PFOA/PFOS deadline to 2031; the secondary-compound limits (PFNA, PFHxS, HFPO-DA, and the Hazard Index) are proposed for rescission in a separate rulemaking, with public comment open until July 20, 2026. Neither proposal is final, so the table above remains the enforceable standard. Utilities exceeding the MCLs must implement treatment, blend with cleaner sources, or take other corrective action. Customer notification requirements apply when MCLs are exceeded.

Treatment technologies recognised by EPA

EPA's technical guidance for the 2024 rule identifies three treatment technologies as effective for PFAS removal at drinking water concentrations:

• Granular Activated Carbon (GAC): The most widely deployed technology at municipal scale. PFAS adsorb to the GAC surface; capacity is finite and depends on Empty Bed Contact Time (EBCT) and bed depth. Residential POE GAC is effective when properly sized.
• Reverse osmosis: The polyamide membrane physically rejects PFAS molecules. Both POE and POU RO are effective. POU RO at the kitchen sink is the most efficient residential implementation.
• Anion exchange (single-use): Some specialty resins capture PFAS by ion exchange. Used in municipal applications; less common in residential systems.

Conventional treatment (sedimentation, coagulation, sand filtration, chlorine disinfection) does not remove PFAS. Boiling concentrates PFAS by removing water as vapour while leaving the persistent fluorochemicals behind.

NSF/ANSI 53 and 58 PFAS certification

PFAS reduction for household filters is certified under NSF/ANSI 53 (activated carbon, carbon block, anion exchange) and NSF/ANSI 58 (reverse osmosis). It appears on a listing as one of three named claims, and a product holds only the ones it was tested for:

PFOA Reduction and PFOS Reduction: the two original single-compound claims, listed separately. The test protocol behind them was built around EPA's 2016 lifetime health advisory of 70 ng/L for the two combined, so it predates the 4 ng/L MCL.

Total PFAS Reduction: the broader claim. NSF's listing footnote defines Total PFAS as seven compounds - perfluoroheptanoic acid (PFHpA), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorobutanesulfonic acid (PFBS) and perfluorodecanoic acid (PFDA). NSF announced the first certification in the world under this claim in December 2023, so it is the newer and broader of the two routes.

NSF P473 is retired. It was a standalone 2016 protocol for PFOA and PFOS reduction, folded into NSF/ANSI 53 and 58 and withdrawn in 2019, with its product listings and references moved across. Michigan's health department dates the cut-over to before March 2019, and NSF's certified products database no longer offers P473 as a searchable standard. Packaging that still cites it is quoting something you cannot verify at source.

A filter advertised as "PFAS removing" without one of those three claims on its listing is making an unverified claim. Look up the product in the NSF certified products database before relying on it; the database lets you search by model and view the specific contaminants the product was tested against, and it names the edition of the standard each claim was evaluated against. Four other ANSI-accredited bodies (CSA Group, IAPMO R&T, UL and WQA) certify to the same standards and keep separate listings, so a filter missing from NSF's database may still be certified elsewhere.

The 2026 proposed revisions

On May 18, 2026, EPA announced two proposed rules that would revise the 2024 regulation. The first would uphold the 4 ng/L MCLs for PFOA and PFOS but give public water systems the option to request two additional years, extending the compliance deadline from 2029 to 2031. The second would rescind the regulations and the underlying regulatory determinations for PFNA, PFHxS, HFPO-DA (GenX), and the Hazard Index mixture (those three plus PFBS), EPA arguing the 2024 rule did not follow the Safe Drinking Water Act's procedural requirements for those compounds.

Both are proposals, not final rules. EPA accepted written comments in the public docket until July 20, 2026, with a public hearing on July 7, 2026. Until either proposal is finalised, the full 2024 rule, including the secondary-compound MCLs and the 2029 deadline, remains the operative federal standard. The picture changes frequently, so verify current MCLs and compliance deadlines at epa.gov/sdwa/pfas before acting. The practical implication for homeowners has been stable so far: the 4 ng/L PFOA/PFOS MCL is not in question, and treatment-technology recommendations are unchanged.

State rules sit alongside the federal rule, but they are not uniformly stricter, and the distinction between an enforceable standard and an advisory value matters. New Jersey has genuine state MCLs, adopted in its June 2020 Safe Drinking Water Act rule amendments at 0.014 micrograms per litre (14 ng/L) for PFOA and 0.013 micrograms per litre (13 ng/L) for PFOS, plus a separate earlier MCL for PFNA. Both figures are above the federal 4 ng/L, so in New Jersey it is the federal MCL that sets the binding number for PFOA and PFOS. California has no state MCL for either compound; it uses non-regulatory notification levels (4.0 ng/L for both PFOA and PFOS, revised October 29, 2025) and response levels (10 ng/L PFOA, 40 ng/L PFOS), which trigger reporting and customer notification rather than a violation. Minnesota publishes health-based guidance values, which its health department describes as guidance rather than enforceable limits. Where a state value is lower than the federal MCL the state value governs; where it is higher, the federal MCL does. Check your own state's drinking water programme rather than assuming either direction.

Practical residential approach

If your CCR or private well test shows detectable PFAS, the response depends on the concentration relative to the MCLs and your risk tolerance.

• Below 4 ng/L PFOA/PFOS: Below the federal MCL. Treatment is optional. Some households choose POU filtration anyway given the MCLG of zero.
• 4 to 70 ng/L: Above the MCL. Treatment recommended. A POU filter at the kitchen sink listed for Total PFAS Reduction, or at minimum PFOA and PFOS Reduction, under NSF/ANSI 53 or 58 is the typical response. Note the ceiling of this band is where the certification protocol was set, not where risk begins: NSF built the PFOA/PFOS claims around EPA's 2016 advisory of 70 ng/L, so a certified filter is verified to get below that figure, not below 4 ng/L.
• Above 70 ng/L: Above the concentration the certification protocol was written to handle in a single pass. Treatment essentially mandatory. POU RO at the kitchen sink plus a whole-house GAC train if budget allows, and check the listed capacity, because claim performance is rated to a stated throughput.
• Above several hundred ng/L: Investigate the source. Industrial groundwater contamination, landfill leachate, or AFFF source proximity may require formal site assessment.

Related: Activated carbon, Reverse osmosis, NSF/ANSI standards explained.