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

What PFAS are

Per- and polyfluoroalkyl substances (PFAS) are a class of more than 12,000 synthetic chemicals containing carbon-fluorine bonds. 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. EPA monitoring data shows detectable PFAS in roughly half of U.S. drinking water systems sampled.

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. 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 P473 and NSF/ANSI 53 PFAS certification

For residential filters, two NSF certifications cover PFAS reduction:

NSF P473 (Drinking Water Treatment Units - PFOA and PFOS): A protocol-level certification specifically for PFOA and PFOS reduction. Products certified to P473 have been independently tested with a defined PFOA/PFOS challenge concentration and verified to reduce both compounds below 70 ng/L (the previous EPA Health Advisory level; the protocol predates the 4 ng/L MCL).

NSF/ANSI 53 with PFAS reduction claim: NSF has been integrating P473 into NSF/ANSI 53 over time. Newer products are certified directly under NSF/ANSI 53 with an explicit PFAS reduction claim. Both designations are functionally equivalent for PFOA/PFOS reduction.

A filter advertised as "PFAS removing" without an NSF P473 or NSF/ANSI 53 PFAS-specific certification 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.

What about the 2025 rollback discussion?

In 2025 there was discussion about regulatory revision of the PFAS rule. As of the April 2026 review date, the 4 ng/L MCLs for PFOA and PFOS remained in effect; some procedural deadlines for the secondary compounds (PFNA, PFHxS, HFPO-DA, PFBS Hazard Index) and the compliance schedule were the subject of regulatory review and litigation. For homeowners, the practical implication is that EPA's 2024 PFOA/PFOS MCL is the current operative federal standard, and treatment technology recommendations are unchanged. Several states (notably California, Minnesota, New Jersey) have set independent state MCLs that are at or below the federal levels; state rules continue to apply regardless of federal proceedings.

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 MCL but below the older Health Advisory. Treatment recommended. NSF P473 or NSF/ANSI 53 PFAS-certified POU filter at the kitchen sink is the typical response.
• Above 70 ng/L: Exceeds even the older Health Advisory. Treatment essentially mandatory. POU RO at the kitchen sink plus a whole-house GAC train if budget allows.
• 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 P473 explained.