Rainwater has been collected and used for most of human history across cultures, and is still used by many today.  But just how safe is it to use?  How clean is it and what can we use it for?

If you’re thinking about installing a rainwater collection system, or are already using an existing one, then you’ve come to the right place.  In this article, we discuss how rainwater is typically collected and used, its purity, and how we can (and can’t) use rainwater in our daily lives.

The answer isn’t all that simple.  While rainwater directly from the sky might be clean, it can pick up contaminants when it travels back down to us, and as a result, we ought to be careful how we use it.

Rainwater Collection

Rainwater collection systems can be a powerful tool for water conservation.  They can also be a necessity for people and places that don’t have access to clean tap or well water from their city, town or region.

Although many different types of rainwater collection systems exist, all systems involve a catchment area (which is the point of entry for the rainwater), a storage tank, and a mechanism for using the water in the tank.  This can be as simple as an open barrel with a sealable spout on the bottom, or as complex as an underground cistern system with water pumps.

People use rainwater for all sorts of activities, including water plants, bathing, drinking, and washing clothes or dishes.  But is all this safe?  We’ve all been told not to drink the water in one place or another, so what about rain water?

rainwater conservation tanks for home water supply

What’s In Rainwater?

Because rainwater is not 100% pure, meaning there’s often more in it than just H2O, we can’t simply assume that it’s always safe to drink.  A heavy rainfall can wash plenty of contaminants into your collection system.  For example, animal droppings can be flushed from your roof or gutters and into your collection tank.

Although in some cases rainwater might contain only a few impurities and therefore be safe for human consumption, there is no way to be certain short of testing for contaminants.  And as they say, it is better to be safe than sorry.

Some may perceive rainwater to be very clean and pure – after all, it comes from a natural process, right?  Although rain is certainly natural, many studies have shown that rainwater across the globe often contains harmful bacteria, and can put those who drink it at increased risk of disease.

Even as it falls to the ground, rainwater can collect dust, smoke, pollen or other contaminants, as the air it passes though isn’t completely pure either.  Of course, this is in large part determined by the area in which you live.

Clear Umbrella with rain drops

Moreover, chemicals, bacteria and parasites can end up in rain water harvesting systems.  Materials used in construction can introduce harmful chemicals into your water tank, like copper, lead or asbestos.  However, using safe materials while building a rainwater collection system can abate some of these concerns.

If you live near a paper mill or chemical treatment plant, it can be especially unwise to drink runoff rainwater or groundwater.  The water in your area may be more prone to pollutants and contaminants.

For all the reasons mentioned above,, the U.S. Centre for Disease Control recommends not drinking, cooking, or brushing your teeth with rainwater. However, they do suggest it can be used for many other activities, like watering plants that you won’t eat, or bathing.  In essence, as long as you’re not ingesting it, you should be fine.

Improving Rainwater Quality

There are many ways to disinfect and otherwise purify rainwater.  However, none of these will ensure that rainwater is totally safe for drinking in all cases.

Common tactics for emergency situations are to treat rain or ground water with iodine or chlorine to disinfect it.  Another common strategy is to boil collected water.  While effective for most pathogens, this will not reduce the harm that can be done by chemical toxicity, and some parasites are highly resistant to chlorine.

Further, many collection systems do not have a filtration feature, which can allow dirt and other particulates to dilute the water in storage.

Rainwater Cleanliness

In summary, while rainwater might seem clean, the studies that have analyzed its composition have found that it can contain many contaminants like bacteria, viruses, parasites and chemicals.  Drinking it, therefore, can put us at an increased risk of disease, and so we should avoid it.  Nevertheless, rainwater can be useful for a host of other activities, like watering the grass or plants you won’t eat, or rinsing yourself off.