Water
PFAS
A large family of synthetic fluorinated compounds used for water, grease and stain resistance. They resist environmental breakdown, which is why they are widely detected in water supplies and why regulation is still developing.
In more detail
PFAS — per- and polyfluoroalkyl substances — are a family of thousands of synthetic compounds built around carbon-fluorine bonds. That bond is among the strongest in organic chemistry, which is what makes the compounds useful for repelling water, oil and stains, and what makes them persist in the environment and in the body long after use.
They reach a house by two routes that are easy to conflate. One is drinking water, where PFAS enter supplies from industrial discharge, firefighting foam use, and land application of biosolids. The other is products: non-stick coatings, stain-resistant textiles, some carpet and upholstery treatments, and certain building materials.
The regulatory picture has been in motion. The EPA finalized national drinking water limits for several individual PFAS in 2024 and has since revisited parts of that rule, and compliance deadlines for utilities run years out — meaning a public system can be legally compliant today and still be working to reduce levels. Any specific number or requirement about PFAS should be read with its date attached, including any quoted here.
Why it matters
Whether a particular house needs to act on PFAS is answerable rather than a matter of opinion: it depends on what is in that supply, which is published for regulated public systems and testable for a private well. That order matters, because PFAS is the contaminant most likely to be used to sell a filter to someone who does not have a PFAS problem, and to be overlooked by someone who does. Treatment that reduces PFAS is not the same as treatment that reduces everything, and no single certification covers the whole family.
The common misunderstanding
That filtered implies PFAS reduction. Most pitcher and refrigerator filters are certified for chlorine taste and some particulates and say nothing about PFAS. Reduction claims are made compound by compound, under a specific certification, at a specific flow rate, for a stated capacity — and a claim covering PFOA and PFOS is not a claim about the thousands of other compounds in the family.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.