Is drinking rainwater safe?

If you stick out your tongue on a rainy day, you might think the drops you’ve tasted are the same as the water that comes out of your tap. But rainwater actually contains many microscopic ingredients that get filtered out before it is pumped into your home.

There are a number of contaminants that can end up in the rainwater, such as bacteria, viruses, parasites, dust, smoke particles and other chemicals, according to the Centres for Disease Control and Prevention(opens in new tab) (CDC). If you collect rainwater from a roof, it could also contain traces left by animals, such as bird poop, and if the roof or drainpipes are old, materials such as asbestos, lead and copper could also end up in your tank. If rainwater is stored in an open container, it also may be full of insects and decaying organic matter, such as dead leaves. For these reasons, the CDC advises against collecting and drinking rainwater but recommends using it for other purposes, such as watering plants.

However, the levels of these contaminants can vary significantly depending on where you live, and the risk of illness depends largely on how much rainwater you drink. If you have a clean collection system and properly sterilize the rainwater, either with chemicals or by boiling and distillation, then most of the impurities can be removed. This has led to a lot of confusion about whether rainwater is unsafe to drink.

What are PFAS

PFAS is a collective term for more than 1,400 human-made chemicals and substances that have historically been used for a range of products, including textiles, firefighting foams, nonstick cookware, food packaging, artificial turf and guitar strings, lead study author Ian Cousins, an environmental chemist at Stockholm University in Sweden, told Live Science in an email.

Past research has shown that these chemicals are extremely toxic and can cause a wide range of problems — including different types of cancer, infertility, pregnancy complications, developmental problems, immune system conditions, and various diseases of the bowels, liver and thyroid — as well as potentially decrease the effectiveness of vaccines in children, Cousins said. PFAS are also likely to cause additional damage to the environment, but this idea has not been studied in as much detail, he added.

Contaminated rainwater

In the study, researchers gathered data from rainwater samples collected across the globe, revealing that PFAS are still abundant in rainwater everywhere on Earth in concentrations above the safety guidelines set by the EPA and other similar regulatory bodies in other countries. Experts had hoped that concentrations of PFAS might have started declining by now, but this is clearly not the case, Cousins said. Instead, researchers think PFAS represent a new planetary boundary, a conceptual limit beyond which something becomes unsafe to humans, that we have already exceeded, he added. The most striking finding was that PFOA levels in rainwater are at least 10 times over the EPA’s safe level at every location sampled on the planet, including the Tibetan Plateau and Antarctica.

Livescience