A new national map spotlights the locations where PFAS toxic chemicals, which have been tied to cancer, have turned up in the water sources that feed public taps.

The chemicals sit under a big umbrella called per- and polyfluoroalkyl substances (PFAS), and scientists have not given them a clean bill of health.

One key correction matters here. Only some PFAS earn the Group 1 carcinogen label, which means they are carcinogenic to humans.

The current consensus puts perfluorooctanoic acid (PFOA) in that box, while perfluorooctane sulfonate (PFOS) is classified as possibly carcinogenic, and not proven in people,.

This is according to a summary by the International Agency for Research on Cancer (IARC) and a companion article in The Lancet Oncology.

Map tracks PFAS in drinking water

Graham F. Peaslee of the University of Notre Dame has tracked PFAS in real world settings for years.

“For a lifetime of exposure at these concentrations in our drinking water, the risk of disease was unacceptably high,” Peaslee explains.

A new Waterkeeper Alliance report collected PFAS samples upstream and downstream of suspected sources in 19 states.

It detected one or more PFAS in 98 percent of waterways tested, and it documented hotspots where levels of PFOA or PFOS exceeded federal limits.

Several cases stand out in the public data set. A Michigan waterway showed PFOA at 44 parts per trillion, and a South Carolina site measured PFOS at 30 parts per trillion.

One North Carolina river reach posted PFOS at 23 parts per trillion with PFOA at 10 parts per trillion.

Sampling focused on places most likely to funnel PFAS into rivers and creeks. That means reaches near a wastewater treatment plant and downstream fields where biosolids are applied as soil amendments.

In these areas, PFAS can ride along in treated effluent and in sludge spread on land.

Limits on PFAS levels in water

In April 2024, the Environmental Protection Agency (EPA) finalized a national drinking water rule that sets legally enforceable maximum contaminant level limits for several PFAS.

For PFOA and PFOS, the limit is 4 parts per trillion, and utilities originally had until 2029 to comply.

Those are tiny numbers, but they matter in risk terms. If a surface water source feeding a public system sits above those limits for PFOA or PFOS, the utility must monitor and, if needed, add treatment so that finished water meets the standard.

On May 14, 2025, the EPA announced it would retain the PFOA and PFOS limits and give systems more time to meet them.

At the same time, it would reconsidering standards for several other PFAS. The agency’s announcement also signaled an intent to extend compliance for PFOA and PFOS to 2031.

That decision drew strong reactions because it leaves many communities managing mixtures with less federal guardrail for the shorter chain compounds.

It also means states and cities may need to decide how far to go on their own, and which technologies to buy.

Exposure adds up

PFAS do not readily degrade in the environment, and they can move from household goods to landfills to wastewater plants, then back into surface water used for drinking supplies.

Even when concentrations are low, steady intake can increase body burdens over time.

“Ideally, we need to strengthen drinking water monitoring and treatment to reduce PFAS exposure through this route,” said Jennifer L. Freeman, a professor of toxicology at Purdue University.

She added that the standards set in 2024 were a step in the right direction and should not be weakened.

A part per trillion is a measurement used for trace pollutants. It helps regulators set enforceable lines, at very low doses, for those contaminants that have health concerns. It also pushes laboratories and utilities to rely on highly sensitive methods to see what is present.

EPA Method 1633, which Waterkeeper’s lab used, reflects that push toward sensitive and standardized testing. It aims to give comparable results across states so a reading in one watershed means the same thing in another.

Local water utilities

If your city relies on a river, reservoir, or well field flagged by the map, your water utility will be testing on a set schedule and reporting results to the public.

You will see whether finished tap water meets federal limits, and what steps the utility is taking if it does not.

Treatment options exist, but they vary in cost and fit. Granular activated carbon, ion exchange, and reverse osmosis all remove PFAS to differing degrees.

Utilities will need to match the options to source water chemistry, budget, and system scale.

PFAS, water, and local governments

Treating one pollutant at a time can miss a major opportunity to reduce overall cancer risk. A peer reviewed study estimates that tackling multiple co-occurring contaminants together could prevent more than 50,000 lifetime cancer cases in the United States.

The logic is simple. Many water systems face several pollutants at once, and integrated treatment can reduce exposures more efficiently than piecemeal fixes.

Expect more state level rules and funding as federal timelines stretch and communities press for action.

Some states have already set their own PFAS limits or passed laws to curb the use of PFAS in consumer products, which reduces what ends up in wastewater and land.

Public water systems will continue the cycle of monitoring, reporting, and upgrading as needed. The best outcome is steady, measurable drops in PFAS at the tap, along with clear communication about progress.

The study is published in Environmental Research.

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