Rainwater almost anywhere on Earth now contains PFAS at levels that exceed the strictest drinking water guidelines, according to a 2022 study from Stockholm University. So as a routine drinking source, untreated rainwater is no longer considered safe under current standards, even in places far from any factory or city.
That conclusion comes from a perspective paper led by Professor Ian Cousins and colleagues, published in Environmental Science and Technology in August 2022. It is worth understanding exactly what the researchers said, because the finding is striking but easy to misread.
The paper, titled "Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS)," compared measured PFAS concentrations in rainwater and surface waters around the world against the most recent health guideline values.
The key result: levels of PFOA and PFOS in rainwater "often greatly exceed" the EPA's lifetime drinking water health advisory levels, and the combined total of four common PFAS in rainwater is frequently above Danish drinking water limits. The team measured this even in remote regions, including Antarctica and the Tibetan Plateau, places with no nearby industrial source.
The reason guidelines are now so easy to exceed is that they have tightened dramatically as the science matured. Cousins noted that the U.S. drinking water guideline for PFOA has dropped by a factor of around 37.5 million over the past two decades. The chemical in the environment did not suddenly multiply. Our understanding of how little is safe changed. Based on the latest U.S. guidance, Cousins said, rainwater everywhere would be judged unsafe to drink.
To see the regulated limits this is measured against, our PFAS overview explains how EPA advisory levels and the 2024 enforceable limits compare.
A few things matter here so this does not turn into panic.
First, "exceeds a guideline" is not the same as "will make you sick today." Modern PFAS guidelines are set with large safety margins against long-term, lifetime exposure and effects like immune and cholesterol changes. Rainwater hitting your skin or the occasional mouthful is not the headline risk. The concern is steady, year-after-year consumption.
Second, most people in developed countries do not drink raw rainwater. The bigger practical takeaway is what the study says about the planet: PFAS now cycle globally through the atmosphere and precipitation, which is why even tap water sourced from rain-fed reservoirs can carry them. Your municipal supply, not the clouds, is where this becomes a daily-life question. You can check what the EPA has recorded for your own water on our home page.
Third, the paper is a scientific perspective arguing that PFAS have crossed a "planetary boundary," not a clinical warning that any single rainfall is toxic. The authors' point is about long-term, irreversible contamination, not acute poisoning.
Some households genuinely depend on collected rainwater, off-grid homes, rural properties, parts of the world without reliable piped water. If that is you, the research suggests you should treat rainwater before drinking it long term.
Rainwater also carries other risks the PFAS story can overshadow, including bacteria, roof runoff contaminants, and heavy metals, which is another reason untreated rainwater is a poor routine drinking source regardless of forever chemicals.
The honest summary is this. The 2022 study did not find that rainwater is acutely dangerous. It found that PFAS are now so widespread, and safe thresholds now so low, that no rainwater on Earth reliably meets current drinking water standards. That is a statement about how far guidelines have fallen and how thoroughly these chemicals have spread, more than about the dose in any one glass.
### Did the study say rainwater will make you sick? No. The 2022 Stockholm University paper compared PFAS levels in rainwater to strict drinking water guidelines and found they exceed them. Exceeding a long-term guideline is a chronic-exposure concern, not a sign that one drink will cause immediate harm.
### Who wrote the rainwater PFAS study? It was led by Professor Ian Cousins of Stockholm University, with co-authors including researchers from ETH Zurich, published in Environmental Science and Technology in 2022.
### Why is rainwater unsafe now when it was fine before? The chemicals did not suddenly increase. Safety guidelines tightened enormously as research revealed harm at much lower doses. The U.S. PFOA guideline alone has fallen by roughly 37.5 million times, so rainwater that once "passed" now exceeds current limits.
### Can I filter PFAS out of collected rainwater? Yes. Reverse osmosis removes 90 to 99 percent of PFAS, and certified activated carbon helps too. Use products certified to NSF/ANSI 53 or 58 for PFAS, and remember rainwater also needs treatment for bacteria and other contaminants.
### Is tap water safer than rainwater for PFAS? Often, but not always. Many utilities now treat for PFAS, but some tap water still shows detections. The only way to know is your local data, which you can check by ZIP code on our home page.
If your drinking water comes from a municipal system rather than the sky, the practical next step is to look up your ZIP code on our home page and see exactly what PFAS and other contaminants the EPA has on record for your supply.