What is Total PFOS and PFOA* and Why Does It Matter?

PFOS and PFOA: The "Forever Chemicals" in Your Tap Water

PFOS (perfluorooctane sulfonic acid) and PFOA (perfluorooctanoic acid) belong to a larger family of chemicals called PFAS — short for per- and polyfluoroalkyl substances. Most people know them as "forever chemicals," and the nickname is earned. These compounds don't break down in the environment or in your body. They've been used for decades in nonstick cookware coatings, water-resistant fabrics, food packaging, and firefighting foam. That foam — called AFFF — is a major reason PFAS ends up in drinking water. Military bases and airports that used it for training and emergencies have contaminated groundwater for miles around their sites. Industrial discharge and landfill runoff carry these chemicals into rivers and reservoirs as well.

The health concerns with PFOS and PFOA are serious and well-documented. Long-term exposure has been linked to kidney and testicular cancer, thyroid disease, high cholesterol, and immune system suppression (according to the EPA and the National Academies of Sciences). Children are especially vulnerable. Studies show that even low-level exposure can reduce vaccine effectiveness in kids, meaning their bodies may not respond as well to routine immunizations (WHO). In pregnant women, PFOA exposure has been associated with preeclampsia and lower birth weight. These aren't rare, extreme outcomes — they're tied to the kinds of levels that appear in real water systems across the country.

Right now, the EPA has set a Maximum Contaminant Level (MCL) of 4 parts per trillion (ppt) for PFOA and PFOS individually under its 2024 final rule. That's a meaningful step forward. But the EWG (Environmental Working Group) sets its health guideline far lower — at just 0.02 ppt — based on the most current research into health effects at trace levels. Of the 48 water systems flagged in this data, all 48 exceed the EWG health guideline. The average detected level is 3.93 ppt, and the highest recorded sample reached 21.4 ppt — more than 1,000 times above the EWG threshold. Even systems that technically comply with the new EPA limit may still carry meaningful health risk under stricter scientific standards.

Wisconsin accounts for 33 of the 48 affected systems, making it the most impacted state in this dataset by a wide margin. Iowa and Washington each show 6 affected systems, with Illinois and Nebraska contributing one each. Wisconsin's high numbers reflect a combination of factors: a strong agricultural and industrial history, legacy use of AFFF at National Guard installations and regional airports, and a dense network of smaller municipal water systems that may lack advanced treatment infrastructure. Washington's affected systems likely connect to military installations in the Puget Sound region, where AFFF use has been extensively documented. Iowa's contamination pattern points to both industrial sites and agricultural runoff from areas where PFAS-containing biosolids — treated sewage used as fertilizer — have been applied to farmland.

The good news is that effective filtration options exist. Reverse osmosis (RO) filtration removes up to 99% of PFOS and PFOA from drinking water, making it the gold standard for home treatment (NSF International). Activated carbon filters — especially those using granular activated carbon (GAC) — also reduce PFAS levels significantly, though not as completely as RO systems. If you're in Wisconsin, Iowa, or Washington, or near a military base or industrial site anywhere in the country, it's worth checking your local water quality report (available through the EPA's ECHO database or your utility's annual Consumer Confidence Report). Echo Water's reverse osmosis systems are independently tested to address PFAS contamination directly at the tap, which is the most reliable point to intercept these chemicals before they reach your glass. Knowing what's in your water is the first step — but filtering it out is what actually protects your family.

Regulatory Standards for Total PFOS and PFOA*

Cities With the Highest Total PFOS and PFOA* Levels

States Most Affected by Total PFOS and PFOA*

Frequently Asked Questions

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