There Is Nowhere on Earth Left Untouched

In August 2022, researchers from Stockholm University and ETH Zurich published a finding that stopped a lot of people in their tracks: there is nowhere on Earth where rainwater would now be considered safe to drink, based on current US EPA health guidelines for PFAS.

Not in the remote Tibetan Plateau. Not in Antarctica. Not over the open ocean. Everywhere they measured, PFAS — the family of man-made “forever chemicals” linked to kidney and testicular cancer, thyroid disease, and immune disruption — were present in rainwater at levels exceeding what the EPA considers safe for drinking water.

This article explains what that research found, why it matters for US tap water drinkers specifically, and what you can actually do about it.

What the Research Actually Found

The peer-reviewed analysis, published in the journal Environmental Science & Technology in August 2022, was led by Professor Ian Cousins at Stockholm University’s Department of Environmental Science. The team reviewed data on PFAS levels in rainwater, soil, and surface water collected across multiple global regions since 2010.

They focused on four well-studied PFAS compounds: PFOS, PFOA, PFHxS, and PFNA — and compared measured concentrations against the latest safety guidelines from the US EPA, the European Union, and other regulatory bodies.

The conclusion was unambiguous. Even in the most remote locations on the planet, PFAS levels in rainwater exceeded EPA health advisory limits. The lowest recorded concentration of PFOA — one of the most studied PFAS compounds — was found on the Tibetan Plateau, and it was still approximately 14 times higher than EPA guidelines. In Antarctica, levels also exceeded those limits.

“Based on the latest US guidelines for PFOA in drinking water, rainwater everywhere would be judged unsafe to drink. Although in the industrial world we don’t often drink rainwater, many people around the world expect it to be safe to drink and it supplies many of our drinking water sources,” Professor Cousins said in the Stockholm University press release accompanying the research.

“There is nowhere on Earth where the rain would be safe to drink, according to the measurements that we have taken,” he told AFP separately.

The researchers concluded that PFAS contamination now represents what they call a “planetary boundary” — a global threshold that, once exceeded, cannot be reversed with existing technology. That boundary, they argue, has already been crossed.

It’s worth noting that Cousins himself was measured about what this means for everyday risk. “I’m not super concerned about the everyday exposure in mountain or stream water or in the food. We can’t escape it… we’re just going to have to live with it,” he told AFP. “But it’s not a great situation to be in, where we’ve contaminated the environment to the point where background exposure is not really safe.” The concern isn’t acute poisoning from a glass of rainwater — it’s the cumulative, inescapable load that now exists at a global level, with no practical way to reverse it.

Why Is PFAS in Rainwater — and Why Isn’t It Going Away?

PFAS were manufactured and used in industrial and consumer products for decades — non-stick cookware, waterproof clothing, food packaging, firefighting foam, stain-resistant carpets. They were valued precisely because they don’t break down. That property also makes them one of the most persistent pollutants ever created.

Once released into the environment, PFAS enter waterways and eventually reach the ocean. From ocean surface water, they are carried into the atmosphere via sea spray aerosols — tiny droplets that evaporate and leave PFAS molecules suspended in the air. Those molecules then fall back to Earth as rain, snow, or dry deposition, contaminating soils, freshwater, and surface water supplies around the world.

This atmospheric cycling means PFAS are continuously redistributed across the planet, regardless of where they were originally produced or used. Even though major manufacturers like 3M phased out certain PFAS compounds two decades ago, their presence in the environment has not meaningfully declined.

“The extreme persistence and continual global cycling of certain PFAS will lead to the continued exceedance of these guidelines,” said Professor Martin Scheringer, a co-author at ETH Zurich. “So now, due to the global spread of PFAS, environmental media everywhere will exceed environmental quality guidelines designed to protect human health and we can do very little to reduce the PFAS contamination. In other words, it makes sense to define a planetary boundary specifically for PFAS — and this boundary has now been exceeded.”

What Does This Mean for US Tap Water?

For most Americans, rainwater isn’t a direct source of drinking water. But that’s not the point. Rainwater feeds the reservoirs, rivers, lakes, and groundwater aquifers that supply public water systems across the country. PFAS entering those sources through atmospheric deposition adds to the contamination already present from industrial discharge, military base runoff, and the application of PFAS-containing biosolids to agricultural land.

EPA monitoring data released in March 2026 shows that around 176 million Americans now have tap water that has tested positive for PFAS — four million more than the previous round of testing. That number continues to rise as utilities complete testing under the national monitoring programme. For the full picture of PFAS rules currently in force and the ongoing legal challenges to rollbacks, see our PFAS rules 2026 explainer.

The research also found that atmospheric deposition leads to soils being “ubiquitously contaminated” with PFAS above proposed guideline values. For private well owners — approximately 13–15% of the US population — this is a particular concern. Well water is not regulated under the Safe Drinking Water Act, meaning there is no federal requirement to test or treat it. PFAS entering soil through rain can leach into groundwater and into private wells without any monitoring or notification. For guidance on well water safety, see our private well water section.

The Regulatory Picture in 2026

In April 2024, the EPA finalised the first-ever national drinking water limits for six PFAS compounds, setting maximum contaminant levels (MCLs) of 4 parts per trillion (ppt) for PFOA and PFOS. In May 2025, the current EPA administration confirmed those two limits would remain in force, but extended the compliance deadline from 2029 to 2031 — and announced plans to rescind limits for four other PFAS compounds: PFHxS, PFNA, GenX, and PFBS.

That rollback is now being contested in court. In January 2026, a federal court declined the EPA’s request to immediately vacate those four limits, and in March 2026 the same court refused a follow-up request to sideline the legal challenge while the agency worked on new rules. As of publication, no revised MCLs for those four compounds have been finalised. The situation is live and changing — our PFAS rules 2026 explainer is updated as developments occur.

The Stockholm University research puts that 4 ppt figure in context. The guideline value for PFOA in US drinking water has declined by 37.5 million times over the past 20 years as scientists have learned more about how toxic these chemicals are at low concentrations. That’s not a sign of regulatory overreach — it’s a sign of how much better our understanding of PFAS toxicity has become.

Some states have set their own, stricter PFAS drinking water standards — Massachusetts, New Jersey, New York, Vermont, Michigan, and others have enforceable limits that go beyond the federal rules. Many states have nothing beyond the federal framework. Our PFAS Protection Map 2026 shows where your state stands.

Can You Filter PFAS Out of Tap Water?

Yes — and this is the most important practical takeaway. While the global spread of PFAS cannot be reversed, the PFAS in your drinking water can be effectively removed at the point of use.

Reverse osmosis (RO) filtration is the most effective method. RO systems force water through a semi-permeable membrane with pores so small that PFAS molecules — along with lead, arsenic, nitrates, and many other contaminants — cannot pass through. Studies consistently show RO systems removing 90–99% of PFAS from drinking water. Look for systems certified to NSF/ANSI Standard 58 for independent verification of performance claims.

Activated carbon filters can also reduce PFAS, particularly solid block carbon filters certified to NSF/ANSI Standard 53 for PFAS reduction. Standard pitcher filters are less effective against the smallest PFAS molecules and should not be relied upon as the primary line of defence against confirmed PFAS contamination.

For filter recommendations matched to your water’s specific contaminant profile, see our water filter solutions guide.

What About Rainwater Harvesting?

Rainwater harvesting — collecting roof runoff for household or garden use — is legal in most US states and has been promoted as a sustainable water practice. The Stockholm University findings add an important caveat: harvested rainwater now carries PFAS contamination, and should not be used as drinking water without treatment through a certified RO or ultrafiltration system.

For garden irrigation, the risk is lower — PFAS in rainwater at current atmospheric concentrations are unlikely to cause immediate harm through incidental skin contact with irrigated plants. But drinking untreated harvested rainwater is not advisable anywhere in the world based on current science.

The Bottom Line

The Stockholm University finding is genuinely significant — not because it means everyone is in immediate danger from rainwater, but because it tells us something important about the scale of the PFAS problem. As Professor Cousins himself acknowledged, the issue isn’t acute risk from any single exposure — it’s that these chemicals have spread so thoroughly through the global environment that even the most remote locations on Earth now carry concentrations above health guidelines, and the water cycle is redistributing them continuously with no reversal possible using existing technology.

For Americans on public water supplies, this is another reason to understand what’s in your tap water — not just what utilities are required to report, but what independent data shows. Use our ZIP code water checker to look up your local supply, and check our full state and city directory for detailed local reports.

The legal limit and the safe limit are not the same thing. The rainwater research is one more reason to take that seriously.

---

Key source: Cousins, I.T. et al. “Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS).” Environmental Science & Technology, 2022, 56(16), 11172–11179. Published by Stockholm University and ETH Zurich. View the study.

This article is for informational purposes only and does not constitute medical advice. For the latest PFAS regulatory developments, see our PFAS rules 2026 explainer. Affiliate disclosure: this site uses affiliate links to water filter products. If you purchase through our links, we may earn a small commission at no extra cost to you. We only recommend products with independent NSF certification.