Is rainwater drinkable?

It depends. “In a big city, rain has a lot of contaminants. In the field and in the forests it is cleaner”, says chemist Adalgiza Fornaro, from USP. But there is no pure rain, composed only of water, anywhere in the world. The reason is simple: when the droplets form, they collect a little bit of everything that is in the surrounding atmosphere. So the rainy cocktail has water, of course, but also solid particles and gases that stay in suspension. “The rain in the countryside is usually rich in calcium and potassium coming from the soil. On the coast, the storms return the sodium that evaporated with the salt in the sea water.” In cities, it is more dangerous.

To give you an idea, rain in São Paulo contains the following poisons: ammonium (which comes from ammonia, a substance produced in decomposition processes, including those linked to the metabolism of living beings), nitrate (resulting from the emission of nitrogen oxides by exhaust), sulfate (originated from sulfur oxides released when fuel is burned), formic and acetic acids (which come from hydrocarbons, also released by cars). Worse: when it rains, tiny grains of dust and soot (that black smoke) or even viruses and bacteria can hitch a ride in the drops. And is this drink bad for you? Well, if I were you, I would prefer a fruit juice… But, as a last resort, drinking rainwater does not pose a major health risk. “These pollutants harm our respiratory system more than our digestive system. In other words, the real problem is in the air we breathe. The rain, after all, helps to dilute them”, says Adalgiza.