Starting From the Compound Universe, Not the Regulatory List
A truly comprehensive PFAS removal standard would be built from the chemistry outward rather than from the regulatory priority list inward. This means beginning with an accounting of the structural diversity that defines meaningful variation in removal behavior — chain length, head group type, charge state, branching, and ether linkages — and designing test protocols that interrogate performance across that diversity, rather than selecting two historically prominent compounds and generalizing from them to the PFAS family.
Such a standard would not need to test all 4,700+ individual PFAS compounds; that is neither technically feasible nor necessary. Instead, it would identify a representative set of structural archetypes that collectively challenge each relevant removal mechanism. A well-designed archetype set of perhaps 20–30 compounds could provide far more meaningful performance characterization than the current two-compound approach.
Minimum Compound Coverage for a Meaningful Standard
At minimum, a comprehensive PFAS removal certification standard should include: the six EPA MCL-regulated compounds (PFOA, PFOS, PFNA, PFHxS, HFPO-DA/GenX, and the PFBS+PFHxS+PFNA hazard index mixture); representative short-chain PFCAs and PFSAs (PFBA, PFPeA, PFHxA for carboxylates; PFBS, PFHxS for sulfonates); at least one ether-containing replacement PFAS (GenX is already included in the EPA set; ADONA would add structural diversity); and representatives of the neutral and zwitterionic precursor classes (a fluorotelomer alcohol and a polyfluoroalkyl phosphate ester).
TFA (C3) occupies a special category: its known zero removability on conventional systems makes it a useful performance boundary marker rather than a practical treatment target, but a comprehensive standard should acknowledge it explicitly rather than leaving it invisible. Including TFA in a test panel and requiring honest disclosure of removal results — even if those results are near zero for most technologies — would provide useful information to purchasers.
Performance Disclosure, Not Just Pass/Fail Certification
A structural improvement to the current certification model would be a shift from binary pass/fail certification (based on achieving a specified removal percentage for the tested compounds) to a performance disclosure model (requiring manufacturers to publish removal efficiency data for a specified compound panel). The disclosure model does not require any technology to achieve comprehensive removal — it requires honest reporting of what each technology achieves.
This approach has precedent in other product category standards. Energy efficiency ratings, fuel economy labels, and noise emission disclosures all provide quantitative performance information without setting a binary pass threshold. A PFAS filter performance disclosure label listing removal rates for a standardized 20-compound panel would allow purchasers to make compound-specific treatment decisions rather than relying on certification marks that reflect a two-compound test.
Precursor Testing as a Long-Term Standard Component
Incorporating precursor compound testing into a comprehensive standard is technically more challenging than terminal PFAS testing but is scientifically justified. The total oxidizable precursor (TOP) assay, which quantifies the precursor content of a water sample by oxidizing all precursors to terminal PFCAs before measurement, provides a practical tool for assessing the precursor burden entering and exiting a treatment system. Including TOP assay results in treatment performance characterization would reveal the fraction of total PFAS-generating potential that a given technology fails to address.
The path from current two-compound certification to comprehensive PFAS performance characterization is not a single regulatory action — it is an incremental expansion of compound coverage, performance metrics, and disclosure requirements that will require coordination among standards bodies, regulators, and the research community. But the scientific foundation for that expansion exists. What is required is the institutional will to build standards that reflect the full scope of the PFAS problem rather than the portion of it that was well-characterized when the first certification protocols were written.