With more than 30 years’ experience in the residential and commercial water treatment space, Mark Nelson is a Class 1 Drinking-Water Operator and a CBWA (Canadian Bottled Water Association) Certified Plant Operator. As founder and president of Nelson Water in Ottawa, Mark focuses on dealing with challenging water treatment system designs for problem water. He also heads the largest water bottling plant in the city of Ottawa with a delivery network throughout the Valley. 

Whether you want to prepare for a natural disaster or enjoy a break in the wilderness, you may have considered whether it is actually safe to drink rainwater. When you consider tap water is often rainwater that’s been collected in a reservoir, it is easy to assume that it must be safe to drink it directly. Unfortunately, this is not the case, so we’ll explore this topic in further detail here. 

Water Treatment

The first thing to appreciate is that while the majority of our tap water is derived from rainwater, it is carefully treated before it ever reaches our homes. The rainwater collected in reservoirs is pumped to a nearby water treatment facility where it goes through a number of processes including disinfection. This is to not only remove any unwanted silt and dirt, but also any bacteria, viruses and other potentially harmful contaminants. The most common form of water treatment is chlorine disinfectant, which is highly effective at killing bacteria, viruses, and pathogens. If left untreated, these contaminants can cause a number of health issues including stomach upsets and digestive issues. Unfortunately, these contaminants are invisible to the naked eye, so there is no way to tell if your water is affected without laboratory testing.

Collecting Rainwater

Even if the rainwater is deliciously pure, the challenge of making it safe to drink is in the collection. When rainwater is collected in barrels, it creates a set of challenges. The actual barrels may harbour things that could be detrimental to health. Damp conditions can encourage mold and mildew to develop, which could contaminate the water. While you may find the musty smell of mildew or mold unpleasant, it is more than an aesthetic issue. Some molds can cause allergic reactions or even respiratory problems when ingested. In fact, there are some molds, under the right conditions, that can produce poisonous substances or “mycotoxins” that can make you very ill.

Even if your barrel is in great condition, the longer the water is sitting, the greater the opportunity for bacteria and organisms to thrive. Generally, flowing water is safer for consumption compared to still water, even water in a clean barrel sitting outside your home.

Natural Purification

So, you may be thinking what about spring water and groundwater supplies? Surely these are also derived from rainwater? The answer is yes, but they differ from collected rainwater in that they are subject to natural purification. Spring water and groundwater supplies push through rocks as they travel through the layers under the surface. This allows the water to be naturally purified for a fresh, clean taste. The water can also collect minerals that may need to be filtered out to improve the taste and aesthetic qualities of the water. For example, hard water is extremely common throughout North America as water is passed through natural deposits of calcium and magnesium in the earth. These minerals are dissolved in the water, but when this water is used in the home, passing through water heaters and other appliances, the minerals can accumulate as scale. This scale collects inside pipes, fixtures, and appliances to compromise performance, efficiency, and lifespan.

Drinking Atmospheric Contaminants

Another issue with drinking rainwater is that you will also be ingesting any atmospheric contaminants. Rainwater passes through the atmosphere, and it will gather up anything that may be swirling around there. This means that rainwater can collect whatever smog, pollution, dust or debris that may be in the air as it falls. In fact, the raindrops can trap these contaminants tightly in each drop. So the rainfall may contain potentially dangerous chemicals that can be harmful to health. You also need to consider that the atmosphere is not static. So, even if you don’t live anywhere near industrial activities that produce chemicals, your rainfall may still be affected by this pollution.


Another consideration that affects the safety of drinking water is the pH. Pure water has a neutral pH, which is beneficial for the body, as human blood is naturally slightly alkaline. Unfortunately, rainwater is typically acidic, with a pH of around 5.6. Drinking acidic water can agitate the normal pH of the body, which can lead to a number of health issues. The symptoms can range from nausea and vomiting to muscle twitching and confusion.

Additionally, acidic water can cause metals to be leached into the water. So, if you collect rainwater in a metal bowl or barrel, it may result in lead or other potentially harmful metals ending up in your drinking water. Since these metals will be difficult to notice with the naked eye, you could be inadvertently ingesting toxic metals.

What’s Rainwater Touched?

Finally, you need to think about what rainwater has touched as it has made its way to your collection container. If the water has passed through plants, run down buildings or even traveled down gutters, it will have picked up dirt and other debris. This will further compromise the safety of rainwater, making it unsuitable for drinking. So, just like you wouldn’t even consider licking a building, you don’t want to drink rainwater that has run down the same dirty, dusty surface.


Basically, while rainwater is a great choice for outdoor cleaning, watering your plants and other activities, it should not be used for drinking water. There are no guarantees that rainwater is clean and the contaminants it collects as it is passing through the atmosphere or being collected may make rainwater unsuitable for ingestion.

Although it is possible to boil rainwater to try to purify it, a more reliable method is a water treatment system.

If you would like to learn more about water treatment systems and devices to ensure that your tap water or private well water is clean and safe to drink, be sure to speak to a water treatment professional. An experienced technician will not only test your water to confirm contaminant levels, but can also guide you through the treatment options best suited to the characteristics of your water.