Have you ever wondered whether or not it's safe to drink rain water? The short answer is: sometimes. Here's a look at when it's not safe to drink rain water, when you can drink it, and what you can do to make it safer for human consumption.
When You Shouldn't Drink Rain Water
Rain passes through the atmosphere before falling to the ground, so it can pick up any contaminants in the air. You don't want to drink rain from hot radioactive sites, like Chernobyl or around Fukushima. It's not a great idea to drink rain water falling near chemical plants or near the plumes of power plants, paper mills, etc. Don't drink rain water that has run off of plants or buildings because you could pick up toxic chemicals from these surfaces. Similarly, don't collect rain water from puddles or into dirty containers.
Rain Water That Is Safe for Drinking
Most rain water is safe to drink. Actually, rain water is the water supply for much of the world's population. The levels of pollution, pollen, mold, and other contaminants are low -- possibly lower than your public drinking water supply. Keep in mind, rain does pick up low levels of bacteria as well as dust and occasional insect parts, so you may want to treat rain water before drinking it.
Making Rain Water Safer
Two key steps you can take to improve the quality of rain water are to boil it and filter it. Boiling the water will kill off pathogens. Filtration, such as through a home water filtration pitcher, will remove chemicals, dust, pollen, mold, and other contaminants.
The other important consideration is how you collect the rain water. You can collect rain water directly from the sky into a clean bucket or bowl. Ideally, use a disinfected container or one that was run through a dishwasher. Let the rain water sit for at least an hour so heavy particulates can settle to the bottom. Alternatively, you can run the water through a coffee filter to remove debris. Although it isn't necessary, refrigerating the rain water will retard the growth of most microorganisms it could contain.
What About Acid Rain?
Most rain water is naturally acidic, with an average pH around 5.6, from the interaction between water and carbon dioxide in air. This is not dangerous. In fact, drinking water rarely has a neutral pH because it contains dissolved minerals. Approved public water could be acidic, neutral, or basic, depending on the source of the water. To put the pH into perspective, coffee made with neutral water has a pH around 5. Orange juice has a pH closer to 4. Truly acidic rain that you would avoid drinking might fall around an active volcano. Otherwise, acid rain isn't a serious consideration.