Contaminant family guide
PFAS Chemicals in Tap Water
PFAS are a large family of persistent synthetic chemicals. Individual compounds have different reference values, monitoring histories, and treatment claims.
What this page can tell you
It explains the family and organizes PurityMap’s published compound records. It does not establish whether any member is present at your tap.
Find the report for your address →Registry counts, not prevalence
What are pfas chemicals?
The family includes many fluorinated compounds designed to resist heat, oil, stains, and water. A family label is useful for orientation, but it is not a substitute for identifying the specific compound in a water record.
Reference values and enforceable limits apply to named PFAS compounds or defined mixtures. PurityMap therefore keeps each compound’s benchmark and measurement context attached to its own guide. In 2024 the U.S. EPA set the first enforceable national limits for several PFAS, including a maximum of 4.0 ng/L each for PFOA and PFOS.
What the national records show
In the 2024 federal UCMR5 monitoring round, PurityMap’s reading of the occurrence data found PFOS above its 4.0 ng/L maximum in 665 of the monitored community water systems in our dataset, PFOA above its 4.0 ng/L maximum in 647, and PFHxS above its reference in 79. These are regulatory exceedances recorded for the monitoring period — not statements about any individual’s health — and the treated water delivered to homes can differ from a monitored result. Reverse osmosis, activated carbon, and anion exchange are the treatment methods most commonly certified to reduce PFAS.
Published compound guides
Open the named compound before comparing a result. References, health context, aliases, and measurement notes belong to the individual record.
CAS 62037-80-3
GenX (HFPO-DA)
Hexafluoropropylene oxide dimer acid (HFPO-DA)
GenX (HFPO-DA) is a newer PFAS "forever chemical" introduced as a replacement for PFOA. It is now federally regulated both on its own and as part of a PFAS hazard index.
CAS 355-46-4
PFHxS
Perfluorohexanesulfonic acid
PFHxS is a shorter-chain PFAS "forever chemical" regulated under the EPA PFAS rule as part of a hazard index alongside other PFAS.
CAS 375-95-1
PFNA
Perfluorononanoic acid
PFNA is a longer-chain PFAS "forever chemical" regulated under the EPA PFAS rule both individually and as part of a combined hazard index with other PFAS.
CAS 335-67-1
PFOA
Perfluorooctanoic acid
PFOA is a per- and polyfluoroalkyl substance (PFAS) — a synthetic "forever chemical" that resists breaking down in water and the body.
CAS 1763-23-1
PFOS
Perfluorooctanesulfonic acid
PFOS is a PFAS "forever chemical" closely related to PFOA, historically used in stain- and water-repellent products and firefighting foam.
Sources named in the compound records
These are source descriptions carried by one or more published compound guides. They are possible pathways, not evidence about a specific water system.
- Fluoropolymer / chemical manufacturing discharge
- Firefighting foam
- Industrial discharge
- Legacy consumer-product manufacturing
- Legacy stain-resistant treatments
How to read a local result
- 1Identify the named analyte
A family name may contain compounds with different standards and health contexts.
- 2Keep the measurement attached
Read the value with its unit, qualifier, sampling period, reporting limit, and source.
- 3Compare only with the stated reference
PurityMap does not turn unlike compound results into a family score or safety verdict.
- 4Verify the relevant treatment claim
A technology name is only a starting point; the product certification must name the compound or reduction claim.
Treatment capabilities in the published records
Named by at least one compound guide in this family. Confirm the exact certified reduction claim before choosing equipment.
Named by at least one compound guide in this family. Confirm the exact certified reduction claim before choosing equipment.
Named by at least one compound guide in this family. Confirm the exact certified reduction claim before choosing equipment.
Treatment relevance is compound-specific and conditional. This list is not a product recommendation and does not mean every technology applies to every member of the family.
Sources and methodology
This page is assembled from PurityMap’s governed contaminant records. Family counts and capability lists are derived only from those published records; local occurrence stays on water-system evidence pages.
How PurityMap analyzes water data →