The Proper Way to Collect Rain Water in an Emergency

In an emergency, collecting rain water can be a very useful way to get pure, safe drinking water. However, there are some things you need to know to ensure its safety.

First, let’s look closer at rainwater. Rain is the source of all fresh water on the planet, including lakes, rivers, streams, glaciers and underground reservoirs. For the most part (I’ll explain in a minute), rain is very pure water.


So where does rain come from? Most rain starts as highly contaminated ocean water.

Ocean water contains high levels of salt and other contaminants. Ocean water is basically poison to us, thus a person stuck on a raft at sea will often die of dehydration. So how does this water turn into high-purity rain water?

It evaporates.

Evaporation means that the water changes from liquid water into water vapor. As soon as this change of state happens, the water molecules let go of the contaminants they are holding onto. The salt and other contaminants stay behind in the ocean, while the pure water vapor rises.

how do i collect rain water
Water’s journey from contaminated ocean water to pure rain water.

Water vapor is just H²O, so it’s pure on a molecular level. The water vapor then condenses into clouds and the clouds move inland. When the conditions are right, this water precipitates into water droplets that fall to the ground; rain.

Rain water is very pure, but…

You’ve probably noticed that the air seems different after a rain shower, right? Cleaner even. That’s because it IS cleaner. Rain cleans out the air. The first few minutes of a shower the rain picks up the dust, smoke and other contaminants that may be in the air. If there are toxins in the air from cars, industry, or even from chemical or nuclear accidents, the rain will absorb these airborne contaminants. So, while rain is very pure water, it can actually become contaminated while it’s falling to earth. This is why we have acid rain. The rainwater itself is not acidic, but rather the contaminants the rain has absorbed are acidic.

But the longer it rains, the cleaner the air becomes and the cleaner the rain becomes.

So this shows us one of the main secrets to properly collecting rainwater; in some cases you may not want to collect the water during the first few minutes of a rain storm. This illustrates one (but not the only) problem with rain barrels, they collect all of the rain water, even the dirty rainwater.

contaminated water

After the 2011 Fukishima nuclear disaster in Japan, for example, people were finding radioactive contaminants in milk in the USA and in Europe. This happened because the explosion caused radioactive iodine and cesium to be shot up into the jet stream, which then carried the radioactive contaminants around the planet. This material would get washed out of the air when it rained. Then cows would eat grass that had a layer of this radioactive material on it or they would drink water that contained it, and this material would then pass through to the milk.

Once rainwater hits the ground, it will absorb small quantities of whatever it comes in contact with. Liquid water, especially when it’s pure, is very effective at absorbing other substances. This is why water is called the universal solvent. In other words, water gets contaminated very easily.

Once on the ground, water then soaks through the soil into our ground water supply or it flows into streams and rivers and begins its downhill journey back to the ocean. All along the way it will absorb much of what it comes in contact with, and by the time it reaches the ocean it could be quite contaminated. Then it reaches the ocean and the process starts over again.


One of the big questions when collecting rain water is how the water is captured, and what the water comes in contact with in the process. Let’s compare these three approaches…

rain pot

APPROACH #1: During a rainstorm you put a clean pot in the rain and if the rain shower drops 4 inches of rain, your pot will have 4 inches of water in it. Not a lot of water, but the water you capture has not touched anything else so there is less chance of contamination.

In most cases, this water should be safe to drink for a day or two without additional treatment. If you are concerned about airborne contaminants, such as toxic smoke or radioactive fallout in your area, wait five minutes after a strong downpour has started before you capture your rain water*. You should use stainless steel, plastic, ceramic, enamel or glass pots for this purpose, but not copper or aluminum.

Also, keep in mind that even though rain water is safe to drink when you first capture it, it won’t stay that way. If you are going to keep the rainwater for more than a day or two you should properly bottle it (see our course on storing water which is available to Premium Members) and add 2 drops of non-scented, liquid, household chlorine bleach to each gallon of water.

Emergency water

APPROACH #2: You have a rain barrel (or cistern or other rain capture system) connected to the downspout of your house. In this case you will be collecting all the water that falls on your roof, so you will capture a lot more water.

BUT…this water has come in contact with your roof and gutters and there is a greater chance of contamination. This could include bird poop, raccoon poop, decaying vegetation, dust, insects, bacteria and viruses. In addition, if your roof contains shingles made with asphalt, asbestos, chemically treated wood shingles or painted metal, toxins could leach into the water (water collection from such roofs are only recommended for non-potable uses). So while this approach increases the quantity of water you collect, you certainly decrease the purity of the water.

Before consuming this water you should treat it with one of the Red Cross recommended methods, boiling, chlorination or distillation, before consuming it (please see our free “basics” course to properly understand emergency water treatment). This water should, however, be fine for bathing, cleaning, washing clothes, etc., although you may want to add chlorine to the water for bathing (follow Red Cross guidelines). Also note that even though it’s not perfect, a rain barrel will most likely provide better water than other sources of surface water, such as a pond or lake.

collecting rain water

APPROACH #3 (HYBRID): The best approach for producing water that you can drink right now is Approach #1. The problem is obvious though, you aren’t going to get much water by just putting out some pots. So how do you capture as much water as possible? What we need to do is increase the surface area of the collection area, but do it in a very clean way. One option would be to use a child’s pool, and this would be a good solution if you were able to get it clean enough. Also, you would want to get the water out of the pool as soon as possible so it wouldn’t get contaminated. Another option is to stretch out a clean tarp or piece of plastic horizontally above the pot and put a weight in the middle to form a “V” shape angle so that it funnels water into the pot. You will have to secure it well, especially if there is a lot of rain. See this picture as an example of how you could do it. This will allow you to collect a greater amount of safe, clean drinking water.


Here’s another way to think about it. In my Storing Water for an Emergency course, I explain that there are two types of stored water; Ready-To-Drink Water and Treat-Before-You-Drink Water. The definitions are quite straightforward…

Ready-To-Drink (RTD) Water is water that you can drink right away without any additional treatment. Commercially produced bottled water is a good example of RTD Water. In Approach #1 and #3 you are producing RTD Water.

Treat-Before-You-Drink (TBYD) Water is water that you have stored away that is not safe to drink, but it can be made safe by boiling, chlorination or distillation. A rain barrel is TBYD Water.


It’s important that you understand how to treat water in an emergency. While the Red Cross recommendations include boiling, chlorination and distillation, only the process of distillation is effective against the full range of contaminants in water. Boiling and chlorination are only effective against biological contaminants. Please refer to our “The Basics” class.

Although rainwater uses the same process of evaporation, condensation and precipitation as distillation, rain water (even in approach #1) won’t be as pure or safe as distilled water. This is simply because distillation happens in a controlled environment, while our natural environment is overloaded with many natural and man-made contaminants.

For more information on this subject, sign up as a Premium Member and you will get full access to my complete Storing Water for An Emergency course, which includes a 12-part video series, a Q&A webinar and a detailed ebook.

* How long you have to wait for rain to clean out the air and become clean and safe depends on many factors, including how hard it’s raining, how much and what type of contaminant is in the air and whether there is a constant source of smoke, such as industry, a chemical fire or even a volcano. You could invest in a TDS purity tester (less than $20) if you want to be able to test your water. This is a judgment call you will have to make. In most cases, I personally would feel comfortable collecting water after 5 minutes of a good downpour.

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