What is Perfluorooctane sulfonate (PFOS)* and Why Does It Matter?

PFOS (perfluorooctane sulfonate) is one of the most persistent man-made chemicals ever created. It belongs to a larger family of chemicals called PFAS — often called "forever chemicals" because they don't break down in the environment or in your body. PFOS was widely used for decades in products like Scotchgard fabric protectors, food packaging, firefighting foam (called AFFF), and industrial coatings. Manufacturing plants, military bases, and airports that used firefighting foam are among the biggest sources of PFOS contamination in drinking water. When these chemicals spill, leak, or wash into the ground, they travel into groundwater and eventually into public water systems.

The numbers tell a concerning story. PFOS currently shows up in 1,160 water systems across the United States. Of those, 971 — more than 83% — exceed the EWG health guideline. The average detected level is 3.308 parts per trillion (ppt), but some systems have recorded levels as high as 250.3 ppt. A "part per trillion" sounds tiny, but PFOS is harmful at extremely low concentrations. The EPA and independent researchers have linked PFOS exposure to immune system suppression, thyroid disruption, elevated cholesterol, liver damage, and certain cancers — including kidney and testicular cancer (National Toxicology Program). Pregnant women and young children face the greatest risk. Even low-level exposure during pregnancy may affect fetal development and reduce how well vaccines work in children, according to the National Institutes of Health.

For years, PFOS existed in a regulatory gray zone. The EPA set a lifetime health advisory of 70 ppt for combined PFOS and PFOA (a related chemical) back in 2016 — a limit many scientists considered far too lenient. In 2024, the EPA finalized its first-ever enforceable limits, setting the Maximum Contaminant Level (MCL) for PFOS at 4 ppt. That's a significant step forward. However, the EWG health guideline is far stricter — just 1 ppt — based on the full body of independent health research. The gap between these two numbers matters. A water system can meet the new EPA standard and still contain PFOS at levels that independent scientists consider unsafe for long-term exposure.

Geography plays a major role in where PFOS contamination is worst. North Carolina leads all states with 157 affected water systems, followed closely by New York with 153 and Texas with 115. Michigan has 79 affected systems, and Illinois has 76. These patterns aren't random. North Carolina has a long history of industrial PFAS manufacturing — including the now-notorious Chemours plant along the Cape Fear River. New York's high numbers reflect decades of military base activity and the widespread use of firefighting foam at airports. Texas and Illinois have large populations, heavy industry, and numerous military installations, all of which contribute to contamination. If you live in any of these states, your water deserves a closer look.

The good news is that PFOS is removable. Reverse osmosis (RO) filtration is the most effective method available to homeowners. A quality RO system removes up to 99% of PFOS and other PFAS chemicals from your drinking water. Activated carbon filters — especially those using granular activated carbon (GAC) — also reduce PFOS levels, though not as completely as reverse osmosis. Standard pitcher filters and basic faucet attachments typically don't cut it for PFAS removal, so it's worth checking a filter's certified performance data before buying. Echo Water's reverse osmosis systems are independently tested and certified to remove PFOS and a wide range of other contaminants, giving you a reliable layer of protection between your family and what's coming out of the tap. If you want to know your specific exposure level, you can request a water quality report from your utility or order an independent water test for PFAS. Knowledge is the first step — and filtration is the practical one.

Regulatory Standards for Perfluorooctane sulfonate (PFOS)*

Cities With the Highest Perfluorooctane sulfonate (PFOS)* Levels

States Most Affected by Perfluorooctane sulfonate (PFOS)*

Frequently Asked Questions

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