Survival Basics

The 3 Basic Ways of Purifying Water

Water is one of our top survival priorities. But it can’t just be any water; it needs to be purified water. If we drink water that hasn’t been purified, there’s a high chance of getting sick from it. While that may not be any worse than vomiting and diarrhea, we need to remember that those can kill you through dehydration. 

In a survival situation, we’ve got to assume that any water source is unsafe to drink, unless we have personally purified it. Even rainwater captured off your roof can be unsafe to drink, as birds poop on your roof. So unless you actually take the time to sterilize your roof, don’t consider that water clean. 

When we’re talking about clean water, we’re not talking about water that isn’t cloudy or that looks clear. Water can be perfectly clear, but unsafe to drink. It can also be cloudy, but still be safe to drink. It’s not the cloudiness that makes water unsafe; that’s just suspended particles. Rather, it’s microscopic pathogens, mostly bacteria, which are too small to be seen with the naked eye. These infect our bodies, causing sickness and even death. 

Because we can’t see those bacteria and we can’t readily test for them, we have to assume that they are there. That’s where the idea of assuming that any water source is unsafe to drink comes from. Fortunately, we only really need to concern ourselves with water that we’re going to drink with, prepare food with or clean the dishes with. 

It’s a good idea to have multiple means of water purifications available to you, even if one of those is your primary. The others can serve as backup, just in case something happens to your primary. 

Let’s explore basic ways of purifying water.


Filtration is probably the most common means of water purification there is, even though it is not technically purification. But for filtration to work, you’ve got to have a water filter that is rated at 0.2 microns or smaller. The “whole house filter” and others are actually just sediment filters, which won’t remove bacteria. Any filter that claims to remove “99.9% of all bacteria” is probably going to be good. 

But filters do have a limitation. That is, they get clogged as they are being used. How clogged they get will depend on how much sediment there is in the water. This is why some systems use multiple filters, with a cheaper sediment filter first, then the bacteria filter afterwards. 

Make sure that you have several spares for any filtration system you are using, unless the filters themselves are backflushable or cleanable. Otherwise, it’s only going to last for a while, then you’ll be without water purification. 


Chemical purification is used in conjunction with filtration in most water treatment plants. The most common purifier used is chlorine, the same thing that is used in swimming pools and found in chlorine bleach. Eight drops of chlorine bleach mixed into a gallon of water will purify it, after being left to sit for 20 minutes.

Chlorine isn’t the only chemical purifier, but it is the cheapest. Iodine works well too, but is considerably more expensive. So are the other chemical purifiers out there. 

Ways of Purifying Water


Pretty much everyone knows that water can be purified by boiling it, but most don’t realize that it doesn’t have to brought all the way up to boiling. All it takes is bringing the water up to 158°F to pasteurize it, killing those microscopic pathogens. That’s what’s been done to the milk you buy in the grocery store. 

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A thermometer can be used to measure the water temperature and so can a WAPI (water pasteurization indicator). This simple device was developed for use in third world countries and consists of a wax pellet in a plastic capsule. The wax melts at 160°F, letting you know when the water is pasteurized.

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