In most cases, rainwater is safe to drink. It can pick up contaminants during its journey but if you’re outside, feel free to stick out your tongue and catch a few raindrops.
If you’re wondering if you can drink rainwater from further downstream, or plan on storing rainwater to use as a potable source of water in your home, it’s worth looking into some of the contaminants and how to resolve them.
Where does rainwater pick up contaminants?
The same quality that makes water the perfect partner for powdered Gatorade or Crystal Light is what can make rainwater unsafe; it’s a solvent (a universal solvent, at that!). Water is uniquely suited to dissolve nearly anything it touches, it can dissolve more substances than any other liquid. While this is an exceptional feature to demand in a cooking ingredient, when it comes to drinking you’re rainwater, it means it can pick up a lot of contaminants.
From the Air
FIrst, rainwater can absorb air pollutants and particles as it falls. This, in and of itself, is not enough to make rainwater undrinkable but you do have to take into consideration where you live. Power plants, factories, and vehicle emissions can all contribute to air pollution that gets picked up by the rain as it falls.
This doesn’t necessarily mean rainwater in your area is bad, the amount of pollution matters. Rainwater typically has a pH of 5.7 and therefore is acidic to start. This is a generally neutral level though. For comparison, black coffee has a pH of about 5 and orange juice has a pH of about 3.5. When it comes to rainwater though, the contaminants it picks up from the atmosphere make it even more acidic. Depending on where you live you might find that your rainwater is more acidic.
It’s unlikely though, that the air is so polluted that you can’t drink the water. The New York Times found in 1989 that Pennsylvania held the record for the most acidic rain at 4.08, less acidic than orange juice.
Your roof is the next most obvious source of contamination. Exposed to the elements, coated in dust, bird droppings, and sometimes moss, it’s more likely that rainwater will pick up debris from your roof than find it’s pH affected. There are two main things you need to consider when collecting rainwater from your roof: debris and roofing material.
There are a lot of opportunities for debris to accumulate on your roof. Overhanging trees can drop branches and leaves and birds droppings can be common on your roof. Neither of these are desirable in your drinking water (I hope). To help manage this you’ll want to do two things.
First, keep as much debris off your roof as you can in the first place. Trim tree branches back to prevent debris from falling on your roof and perform regular cleanings.
Second, if you are capturing and storing rainwater, you can install leaf strainers or rainwater diverters that will prevent the debris from entering your tank. Whether you have a tree overhanging your roof or not, this is something that you should include in your system.
How dangerous can rainwater be?
As I stated at the beginning, in most cases, rainwater is drinkable. Rainwater has never fallen with a pH more acidic than orange juice and, barring any contaminants getting into your tank, it should be safe to drink rainwater.