How the 2024 EPA MCL Structure Defines Compliance Requirements
The EPA 2024 National Primary Drinking Water Regulations for PFAS established maximum contaminant levels on a per-compound basis: 4 ppt for PFOA individually, 4 ppt for PFOS individually, 10 ppt for PFNA individually, 10 ppt for PFHxS individually, and 10 ppt for HFPO-DA (GenX) individually. A sixth provision establishes a hazard index for mixtures of PFNA, PFHxS, PFBS, and PFHpA that are present in combination. This regulatory structure is compound-specific: compliance is assessed by measuring each compound in finished water and comparing it to its individual MCL. A system that meets the PFOA MCL but exceeds the PFNA MCL is not in compliance, regardless of total PFAS concentration.
This per-compound regulatory structure has a direct corollary for filter certification: compliance cannot be demonstrated by any single certification mark that does not include compound-specific performance data for all regulated compounds. Yet the most widely deployed filter certification standard — NSF/ANSI 53 — tests and certifies performance for only two of the six individually regulated PFAS (PFOA and PFOS). A facility deploying NSF 53-certified point-of-use devices to meet the 2024 MCLs for PFNA, PFHxS, and GenX is operating without compound-specific verification for four of the six regulated analytes.
The Mismatch Between Regulatory Scope and Certification Scope
This mismatch is not a regulatory oversight — EPA’s authority covers contaminant levels in finished drinking water delivered by public water systems, while NSF International sets product performance standards through a private, consensus-based process. The two frameworks operate on different timelines and different governance structures. EPA can promulgate new MCLs within a regulatory cycle of two to three years; NSF standard revisions require committee consensus, public comment, manufacturer testing, and accreditation body approval, typically spanning three to five years.
For water engineers and compliance officers, the practical consequence is that they are currently operating in a period where the regulatory compound list has outpaced the certification compound list. The four-compound gap (PFNA, PFHxS, GenX, and the hazard index compounds) represents real regulatory liability for facilities that rely exclusively on NSF 53 certification as their PFAS compliance documentation. Until NSF/ANSI 53 is revised to include the 2024 MCL compounds, facilities need supplementary compound-specific test data from KCL, WQA supplementary panels, or independent laboratory verification.
Building a Per-Compound Compliance Documentation Framework
A technically defensible compliance documentation framework for PFAS point-of-use or point-of-entry filtration should organize performance data by compound, not by certification mark. For each regulated compound, the documentation should include: the source water concentration (measured by a certified laboratory using an appropriate EPA method), the expected effluent concentration based on filter performance data, and the basis for that performance expectation (certification test report, KCL compound-specific data, independent laboratory verification, or engineering calculation). The MCL is then compared against the expected effluent concentration to confirm the margin of safety.
For compounds where no certified performance data exists (PFNA and PFHxS under current NSF 53), two options are available: obtain compound-specific test data from an accredited laboratory using the actual filter product and a representative challenge water, or use conservative assumptions based on published literature for the filter technology in question (acknowledging the lower adsorption affinity of these compounds compared to PFOA and PFOS). The first option is preferable for regulatory defensibility; the second is acceptable as a screening approach to identify products requiring further testing.
What Per-Compound Certification Will Look Like Going Forward
The trajectory of PFAS filter certification is toward per-compound verification, driven by both regulatory expansion and growing procurement sophistication. NSF is developing revisions to NSF/ANSI 53 and considering a new supplementary certification category specifically for the 2024 MCL compounds. Some advanced filter manufacturers are proactively commissioning compound-specific testing through KCL and other accredited bodies to build ahead of the certification standard revision. The manufacturers who invest in this testing infrastructure now will have a significant competitive advantage when procurement specifications are updated to require per-compound data.
For facilities making filter procurement decisions in the 2024-2026 window, the recommendation is to require per-compound performance documentation in procurement specifications, weight compound-specific test data heavily in evaluation scoring, and plan for re-evaluation of installed products when the NSF/ANSI 53 revision is finalized. A filter that performs well for PFOA and PFOS today may not meet the revised certification threshold for PFNA and PFHxS when those compounds are formally incorporated into the standard.