Rainwater is not safe to drink anymore due to 'forever chemicals'

And it's valid even in remote areas of the world.
Mert Erdemir

Have you ever wondered about the taste of rainwater? Well, it might be tasty or not, but a new study suggests that it's definitely unsafe to drink, even in remote areas of the world.

A new study conducted by researchers from Stockholm University and ETH Zurich suggests that rainwater contains per- and poly-fluoroalkyl substances (PFAS), human-made chemicals used in a wide range of consumer and industrial products. They are known as ‘forever chemicals’ because they don’t decompose in the environment. But what the study demonstrates is that these "forever chemicals" are now spread globally in the atmosphere so that they can be found in the rainwater and snow in even the most remote and isolated locations on Earth.

Declining guideline values

As stated in the press release, the guideline values for PFAS in drinking water, surface waterways, and soils have drastically lowered over the past two decades due to new insights into their toxicity. So, the levels in environmental media are currently almost always over the recommended range. In relation to that, the study claims PFAS defines a new planetary boundary for novel entities that ha been exceeded.

“There has been an astounding decline in guideline values for PFAS in drinking water in the last 20 years. For example, the drinking water guideline value for one well-known substance in the PFAS class, namely the cancer-causing perfluorooctanoic acid (PFOA), has declined by 37.5 million times in the U.S.,” said Ian Cousins, the lead author of the study and professor at the Department of Environmental Science, Stockholm University.

“Based on the latest U.S. 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,” Cousins continued.

How risky are these "forever chemicals"?

A review from the U.S. Centers for Disease Control and Prevention (CDC) states that the possible health risks of PFAS exposure may be underestimated, outlining them as cancer, liver damage, fertility problems, and increased risk of asthma and thyroid disease.

“It cannot be that some few benefit economically while polluting the drinking water for millions of others, and causing serious health problems. The vast amounts that it will cost to reduce PFAS in drinking water to levels that are safe based on current scientific understanding need to be paid by the industry producing and using these toxic chemicals. The time to act is now,” points out Dr. Jane Muncke, Managing Director of the Food Packaging Forum Foundation in Zürich, Switzerland, and not involved in the work.

Results of the study have been published in the journal Environmental Science & Technology.


It is hypothesized that environmental contamination by per- and polyfluoroalkyl substances (PFAS) defines a separate planetary boundary and that this boundary has been exceeded. This hypothesis is tested by comparing the levels of four selected perfluoroalkyl acids (PFAAs) (i.e., perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic acid (PFNA)) in various global environmental media (i.e., rainwater, soils, and surface waters) with recently proposed guideline levels. On the basis of the four PFAAs considered, it is concluded that (1) levels of PFOA and PFOS in rainwater often greatly exceed US Environmental Protection Agency (EPA) Lifetime Drinking Water Health Advisory levels and the sum of the aforementioned four PFAAs (Σ4 PFAS) in rainwater is often above Danish drinking water limit values also based on Σ4 PFAS; (2) levels of PFOS in rainwater are often above Environmental Quality Standard for Inland European Union Surface Water; and (3) atmospheric deposition also leads to global soils being ubiquitously contaminated and to be often above proposed Dutch guideline values. It is, therefore, concluded that the global spread of these four PFAAs in the atmosphere has led to the planetary boundary for chemical pollution being exceeded. Levels of PFAAs in atmospheric deposition are especially poorly reversible because of the high persistence of PFAAs and their ability to continuously cycle in the hydrosphere, including on sea spray aerosols emitted from the oceans. Because of the poor reversibility of environmental exposure to PFAS and their associated effects, it is vitally important that PFAS uses and emissions are rapidly restricted.

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