Is rainwater safe to drink?
If you stick your tongue out on rainy day, you might think the drops you’ve tasted are same as water from your tap. However, rainwater contains many microscopic ingredients that are filtered out before being pumped into your home.
So is it safe to collect and drink rainwater?
According to the Centers for Disease Control and Prevention(CDC), a variety of contaminants such as bacteria, viruses, parasites, dust, smoke particles, and other chemicals can end up in rainwater. If you collect rainwater from a roof, it may contain animal traces like bird poop, and if the roof or drainpipes are old, materials like asbestos, lead, and copper may end up in your tank. If rainwater is collected in an open container, it may be contaminated with insects and decaying organic matter, such as dead leaves. For these reasons, the CDC advises against collecting and drinking rainwater, instead recommending that it be used for other purposes such as watering plants.
The levels of these contaminants, however, can vary significantly depending on where you live, and the risk of illness is largely determined by how much rainwater you drink. Most impurities can be removed if you have a clean collection system and properly sterilize the rainwater, either with chemicals or by boiling and distillation. This has created a great deal of uncertainty about whether rainwater is safe to drink.
However, in this day and age of man-made chemicals, there is a new danger associated with drinking rainwater. Researchers discovered toxic PFAS (per- and polyfluorinated alkyl substances) in rainwater all over the world in a study published in the journal Environmental Science & Technology in August 2022. These findings indicate that rainwater is unquestionably unsafe to drink, particularly if it is untreated.
What exactly are PFAS?
According to lead study author Ian Cousins, an environmental chemist at Stockholm University in Sweden, PFAS is a collective term for more than 1,400 human-made chemicals and substances that have historically been used in a variety of products, including textiles, firefighting foams, nonstick cookware, food packaging, artificial turf, and guitar strings.
However, “the current understanding of biological impacts is primarily based on studies of four perfluoroalkyl acids (PFAAs),” a subgroup of PFAS, according to Cousins. Perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic acid (PFNA) are among the PFAAs studied.
Previous research has shown that these chemicals are extremely toxic and can cause a wide range of problems, including various types of cancer, infertility, pregnancy complications, developmental problems, immune system conditions, and various diseases of the bowels, liver, and thyroid, according to Cousins, as well as potentially decreasing the effectiveness of vaccines in children. PFAS are also likely to cause additional environmental damage, but this idea has not been thoroughly researched.
PFAAs and most other PFAS have been banned or heavily restricted in the last 20 to 30 years, with the exception of China and a few other Asian countries. The health guidelines surrounding PFAS have also been updated to reflect the toxicity of the chemicals. According to the researchers, the safe level of PFOA exposure determined by the Environmental Protection Agency (EPA) in the United States is 37.5 million times lower than it was previously.
PFAS don’t degrade easily, so they remain in the environment for a long time after they are produced and are just as toxic. As a result, scientists have dubbed PFAS “forever chemicals.”
Researchers gathered data from rainwater samples collected around the world for the study, which revealed that PFAS are still abundant in rainwater everywhere on Earth in concentrations above the EPA and other similar regulatory bodies in other countries.
Experts had hoped that PFAS concentrations would have begun to decline by now, but this is clearly not the case, according to Cousins. Instead, researchers believe that PFAS represent a new planetary boundary, a conceptual limit beyond which something becomes dangerous to humans, which we have already crossed, he added.
The most startling discovery was that PFOA levels in rainwater are at least ten times higher than the EPA’s safe level in every location sampled, including the Tibetan Plateau and Antarctica.
According to Cousins, the researchers are still unsure how PFAS are transported to the most remote parts of the globe. The team hypothesizes that PFAS on the ocean’s surface are reinjected into the atmosphere by ocean spray and then transported to other regions, where they fall as rain; future research will test this hypothesis. Cousins added that PFAS may still be leaking into the environment from landfills.
It is too early to predict the global public health effects of PFAS-rich rainwater, but they may already be underway. “We’ve been exposed at even higher levels for the past 20 to 30 years,” Cousins explained. “We’re only now getting a better understanding of the potential consequences of that exposure.”
The impact of PFAS will be greater in developing countries where millions of people rely on rainwater as their sole source of drinking water. However, even in developed countries, such as Western Australia, drinking rainwater is still surprisingly common.
Even if rainwater is treated properly, there is no guarantee that PFAS will be removed. PFAS can also be found in low levels in tap and bottle water, though these levels are usually safe.
PFAS levels will decrease as they cycle into deep ocean, but this will be slow process that could take decades.