Chemicals found in tap water linked to a 33% increase in cancer rates

You’ve probably heard of PFAS “forever chemicals” – synthetic chemicals used to resist water, grease, and heat. They’ve been in nonstick coatings, stain-repellent fabrics, and older firefighting foams for decades.

They don’t break down easily, and that staying power means they can build up in soil, water, wildlife, and people.

A recent and disturbing analysis links polyfluoroalkyl substances (PFAS) detections in public drinking water to higher cancer rates in certain parts of the United States.

The headline number is blunt: exposure to these chemicals in tap water is associated with up to a 33 percent higher cancer risk. That statistic sets off alarms, as it should, but the details matter for what we do next.

Linking PFAS to cancer

After years of debate about how to regulate PFAS, researchers at the Keck School of Medicine at the University of Southern California (USC) looked for patterns across the country.

Their core question was practical: in places where public drinking water systems detect PFAS, do those places also report higher rates of certain cancers?

The scientist leading the work is careful about what the data can and cannot show. He warns that additional restrictions may be necessary to protect public health.

“When people hear that PFAS is associated with cancer, it’s hard to know how it’s relevant,” Dr. Li said. “These findings allow us to draw an initial conclusion about the link between certain rare cancers and PFAS.”

How the study was done

This was an ecological study, which means the unit of analysis was the place, not individual people.

The team pulled county-level cancer incidence – new cases per year, adjusted for age – then matched those figures with water-testing results from federal monitoring programs.

One program in the 2010s tested thousands of public water systems for various PFAS. A newer, more sensitive round of testing has been rolling out, providing sharper detection.

Using both datasets, the researchers marked counties where specific PFAS showed up in public water and noted where any measurements exceeded today’s strict national limits.

They then ran statistical models that controlled for other forces known to influence cancer rates, including smoking, obesity, income, urban-rural differences, and air pollution.

Sex, cancers, and PFAS

Counties with PFAS detections generally had higher incidence rates for several cancer groups.

Patterns were seen in digestive system cancers, thyroid and other hormone-related cancers, respiratory cancers, and some head-and-neck cancers.

The increases weren’t massive jumps, but they appeared often enough to raise concern. When the data were split by sex, some differences emerged.

In men, associations leaned toward kidney and bladder cancers, certain nervous system cancers, leukemia, and soft tissue cancers. In women, the clearest signal was thyroid cancer, along with oral cavity and soft tissue cancers.

Cancer biology fits PFAS traits

PFAS are a large chemical family, but several members share traits that could connect to cancer biology.

Some interfere with hormone signaling, especially in the thyroid. Others stress the liver and disrupt how the body manages fats.

There’s evidence that certain PFAS promote chronic inflammation and influence how genes are switched on and off over time.

None of these mechanisms, on their own, prove causation, but they make the observed associations plausible rather than random.

What the numbers mean

The study offers national, population-level estimates: if the associations reflect real effects, the number of cancer cases per year linked to PFAS in drinking water could reach very high numbers in the US alone.

Treat those figures as ballpark, not precise counts. They’re most useful for policy: where to prioritize treatment, how fast to upgrade systems, and which communities need the most attention.

The policy context is shifting. The United States now sets strict legal limits for several PFAS in drinking water, and utilities are ramping up compliance.

As Dr. Li notes, those limits may still be too lenient, and further tightening could be warranted as evidence grows.

Removing PFAS at the root

Utilities must publish water quality reports, and many now include PFAS monitoring results.

Check your local report and see what’s been measured, how often, and what actions are underway. If your system is upgrading treatment, look for timelines and interim steps.

At home, point-of-use filters can help if they are certified to reduce PFAS. Activated carbon and reverse osmosis units are the most common options.

Maintenance matters; filters that aren’t replaced on schedule lose effectiveness. If you rely on a private well, consider testing through a certified lab and consult your health department about options if PFAS appear.

Technologies exist and keep improving. Granular activated carbon, ion exchange resins, and high-pressure membranes can capture or remove many PFAS.

Each comes with trade-offs in cost, energy, and waste handling. Systems need steady monitoring because PFAS mixtures vary by source and season.

The right design for a small rural system may differ from that for a large urban plant, but both can get results with careful engineering and oversight.

PFAS, cancer, and the future

To sum it all up, this study directly linked PFAS in public drinking water with higher rates of several cancers at the county level – up to 33% higher.

The study stops short of proof for individuals, but the pattern is consistent with how these chemicals behave in the body.

Keeping up strong testing, enforcing modern limits, upgrading treatment where needed, and pushing for targeted, person-level studies will help turn a broad signal into clear guidance.

Communities deserve to know what’s in their water and what’s being done about it – and they deserve steady progress that reduces risk over time.

The full study was published in the Journal of Exposure Science & Environmental Epidemiology.

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