PFOS in Tap Water
PFOS is a PFAS "forever chemical" closely related to PFOA, historically used in stain- and water-repellent products and firefighting foam.
Also known as forever chemical
PFOS across 4,194 city records
Each bar counts cities whose system reported a highest result in that range. The dashed line is the 4.0 ng/L federal MCL (2024). A position is not a verdict on the water.
- 764 detected, plotted below
- 3,396 below the lab’s reporting limit
- 34 no result on record
Firefighting foam and industrial/consumer product manufacturing; highly persistent.
- 1Firefighting foam
- 2Industrial discharge
- 3Legacy stain-resistant treatments
Most affected: Infants, pregnant people, and immunocompromised individuals.
A result is read with its context
Reported here from EPA UCMR5 occurrence monitoring. A non-detect reflects the method reporting limit, not a guarantee of zero. PurityMap publishes this substance per water system on individual system and city-report pages, where the source dataset provides a value.
- Above reference
- Evidence exceeds a reference level.
- Detected
- This substance was found in the monitoring record. Being present is not the same as being above a reference level, and this signal does not say which.
- Not detected
- Somebody looked and the laboratory reported nothing above its reporting limit. This is a result, and it is not the same as nobody looking.
- Not monitored
- No sampling for this substance has been reported for this system. Nothing is known either way, and an empty row is not a clean one.
746 cities above the federal limit
- AberdeenNC→
- AberdeenMD→
- AbileneTX→
- AbingtonMA→
- Acton DistrictMA→
- AdelantoCA→
- AlabasterAL→
- AlbemarleNC→
- Albertson WdNY→
- AlbertvilleAL→
- AlexandriaMN→
- AllentownPA→
- AltonTX→
- AmblerPA→
- AmeliaOH→
- AnaheimCA→
- AndersonIN→
- AngierNC→
Showing 18 of 746. Open a state for its full list. A system-level result, not a measurement of any single home.
What can carry a PFOS reduction claim
- Reverse osmosis
Semi-permeable membrane separation removing dissolved minerals, heavy metals, and persistent fluorinated chemicals down to 0.0001 microns.
- Activated carbon (GAC)
Highly porous adsorption media targeting chlorine, disinfection byproducts, volatile organic compounds, and organic chemicals.
- Anion exchange
Synthetic polyvalent resin beads that exchange unwanted dissolved ionic contaminants for harmless benchmark ions.
Boiling does not remove a dissolved chemical compound and can concentrate it. Many pitcher and refrigerator filters carry no verified claim for a compound like this at all.
A finding establishes the need, the need names the capability, the capability requires a verified certification. No product appears before that sequence completes. Filter Finder →
Frequently asked
Answers cite the same records as the page. How PurityMap analyzes water data
PFOS is a PFAS "forever chemical" closely related to PFOA, historically used in stain- and water-repellent products and firefighting foam.
The enforceable federal limit is 4 ng/L (MCL); MCLG of 0. PurityMap reads every measurement against its stated benchmark and never sets its own.
Firefighting foam, Industrial discharge, Legacy stain-resistant treatments.
PFOS is linked in studies to immune, thyroid, liver, and developmental effects and to certain cancers. Like PFOA, it bioaccumulates, and the enforceable limit is set near the lowest measurable level.
Treatment technologies commonly certified to reduce PFOS include Reverse osmosis, Activated carbon (GAC), Anion exchange. Match the exact certified claim to your water before buying. Holding a format is not the same as holding the claim.
In PurityMap's published record, PFOS was detected in 764 cities (of 4,160 with a result) across 45 states, with 746 above the federal limit. This is the scope of our record, not a national prevalence estimate.