How to Purify Drinking Water (This Could Save Your Life)

One major concern after a disaster is how to purify drinking water to make it safe. Getting this wrong could result in painful illnesses or even death.

The best way to purify drinking water is using multiple steps that include basic filtering, chemical treatment (or boiling), and then activated charcoal. This gives you the best chance of removing all contaminants and making the water safe to drink.

This article will cover each of these steps in greater detail along with different ways that you can accomplish them.

What You Need to Remove From Your Water

The first thing you need to understand about purifying drinking water is that you’ll need to remove multiple kinds of contaminants. Some of these are simply irritating while others could cause you significant discomfort or harm. Here are the contaminants that you would likely need to remove:

Large Debris and Sediment: The first thing that you need to remove from your water is large debris or sediment. Larger debris can consist of things like grass or pebbles, while sediment can be very fine grains of sand.

Bacteria: If left in your drinking water, different kinds of bacteria can cause various health problems. Most of these are gastrointestinal and cause symptoms such as diarrhea and/or vomiting. Cholera and typhoid fever are examples of illnesses caused by water-borne bacteria.

Protozoa: Protozoa are single-cell organisms similar to bacteria, however, they are slightly larger and contain additional cell structures, such as a nucleus. They too can cause various diseases, one of the most common being giardiasis, which causes severe diarrhea among other symptoms.

Viruses: The smallest biological contaminants that you may need to remove from drinking water are viruses. They’re so small that most water filters simply will not be able to remove them. Viruses are more common in populated areas and can include rotavirus, norovirus, Hepatitis A, and more.

Chemicals: Various chemicals, such as petroleum, pesticides, and herbicides may find their way into your drinking water. This can happen due to runoff from agricultural areas or water from roadway storm drains feeding into local water sources.

Stage 1: Pre-Filtering

Emergency Water Prefilter

The first thing you should do when purifying drinking water is to attempt to remove as much large debris as possible. This will make the rest of the process slightly easier and will help you extend the life of your main water filters. At the very least, it will reduce the amount of maintenance you need to perform on them.

Pre-filtering can be as simple as draping a pillowcase over the top of a bucket and pouring the water through it. The pillowcase will catch things like grass and pebbles so that you can simply discard them.

If you want to do a more thorough job, you can assemble a basic filter using something like a 5-gallon bucket or large plastic bottle. Pack the bucket or bottle with multiple layers of sand, activated charcoal, pebbles, and relatively small rocks. From top to bottom, it should be rocks, small pebbles, sand, and activated charcoal.

Using an improvised filter like that isn’t entirely necessary if you follow the rest of the steps but it can help extend the life of your other filters and give you a little more peace of mind. However, I wouldn’t count on it as a standalone water purification method.

Stage: 2: Filtering

Water filter attached to bucket
Sawyer Tap filter attached to a bucket using a spigot kit.

The next thing you’ll need to purify your drinking water is a good-quality water filter. There are several options on the market, however, Sawyer filters, such as these, are a good balance between quality and price.

Sawyer water filters remove virtually all sediment, bacteria, and protozoa because of their 0.1-micron absolute pores. This means that no pore in the filter is larger than 0.1 microns, so nothing larger than that will be able to pass through it. The only things that they can’t remove are chemicals, viruses, and radiation. (Radiation is a whole other topic and will be discussed briefly at the end of this article.)

You have a couple of different options when it comes to how your Sawyer filter is configured. Most of their filters are small and designed to be carried in a bug-out bag or hiking backpack. You can get the Sawyer Mini as part of a gravity system which consists of the filter and a bag to hold water before it’s filtered. You can find it by clicking here.

The option that I went with was their Sawyer Tap filter. It’s designed to slip over the faucet on your sink during boil water notices or if you’re traveling in an area with questionable running water. For times when I have no running water, I’ve installed a spigot like this one on a 5-gallon bucket. This will allow me to attach the Sawyer Tap filter’s spigot adapter to the bucket and use it as a gravity filter.

Using either the dedicated gravity filter or the Sawyer Tap attached to a bucket will remove any sediment that your prefiltering missed and remove virtually all of the bacteria or protozoa that may be present.

Recommended: Best Water Filters for Preppers and Survival

Stage 3: Chemical Treatment or Boiling

The next thing you’ll need to do to purify your drinking water is to chemically treat it or boil it. These methods will help remove any biological pathogens that may still be present after filtering, most notably viruses.


The most effective way to remove biological contaminants from your water is to boil it. A good rolling boil will either kill or inactivate viruses and other microorganisms. Boil times are one minute for altitudes under 2,000 meters and 3 minutes for higher altitudes. It’s especially helpful if water is contaminated with pathogens that may be resistant to chemicals or UV light.

The main problems with boiling are that you’ll need fuel for a heat source and that it won’t remove chemicals or sediment. However, there are many ways that you can produce enough heat to boil water and the other steps of this process should remove any sediment or chemicals that may be present.

Fuel-based cooking methods such as propane stoves, butane stoves, and grills are good options since they use tools and fuel sources you may already have. Other fuel-based cooking methods like Jetboil systems and alcohol stoves aren’t as common, but they are more portable.

If you want something for more long-term disaster situations, Kelly Kettles and various rocket stoves will allow you to use commonly-available natural materials to boil water and cook. Kelly Kettles are especially useful for boiling water since they were specifically designed for that task.

Chemical Treatments

Like boiling, chemical treatments can do a good job removing most of the remaining biological contaminants from your water. However, some pathogens such as Cryptosporidium in the cyst stage are resistant to chemical treatment methods.

The best time to use chemical treatment methods is if you’re in a situation where boiling water is impossible or could threaten your security. Starting a fire in certain weather conditions can be difficult. Also, most fires are visible from a considerable distance, which may make starting one undesirable if you are trying to avoid others.

Chlorine bleach is probably the most common way to chemically treat water. When using bleach, make sure to purchase regular disinfecting bleach. Other kinds have scents or other chemicals that shouldn’t be added to drinking water.

If using 6% bleach, add 8 drops to every gallon of water. For 8.25% bleach, use 6 drops for every gallon. If the water is cloudy, colored, or very cold, use double these amounts. You can find more information about using bleach to disinfect drinking water by clicking here.

Other chemical water treatment methods include household iodine, water purification tablets, or producing a bleach solution using granular calcium hypochlorite. You can find more information about them from the link above.

Stage 4: Activated Charcoal or Carbon

The last stage of purifying your drinking water should include activated charcoal or carbon. Probably the easiest way to do this is to use a gravity filter that utilizes these kinds of media. This will help remove chemicals from your water, including chlorine bleach from the previous step.

Filters such as those produced by Berkey use activated carbon in their black filtering elements and will work well for this purpose. Many of you are probably wondering why you should go through all of this trouble when those filters should remove pretty much anything on their own.

The reason for this is redundancy. If you’re in a long-term grid-down scenario or even something like a major storm, there’s a very good chance that many kinds of contaminants will be present in nearby water sources. Having multiple ways to remove most of the contaminants is a good way to ensure that if one method fails, one of the others will pick up the slack.

Related: Berkey Water Filter Review

A Note About Radiation

Removing radiation from water can be more challenging than removing other types of contaminants. Fortunately, events such as nuclear strikes and nuclear power plant meltdowns are relatively uncommon.

If you do find yourself in a situation where you need to remove radiological contamination from water, the most common ways to do this are reverse osmosis and reverse ion exchange. Most reverse osmosis systems are designed to integrate with your home’s plumbing system.

If you need something portable, Seychelle offers a filtering water bottle that is marketed as being able to remove radiological contaminants. This is done through what they refer to as an “exclusive ionic-adsorption micro-filtration system”.

However, at the end of the day, it’s best to avoid drinking water with radioactive contamination. Keeping a good stockpile of stored water and living away from potential nuclear targets or nuclear power plants are both excellent ideas.

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