How to Purify Water: 11 Ways to Make Your Water Safer to Drink


Of all our survival needs, water is near the top of the list. In fact, only shelter, the ability to keep our bodies warm, outdoes water as a survival need. We must consume water daily for our bodies to use, and if we go more than three days without it; chances are, we’ll die.

But not just any water will do. Water can carry a whole host of microscopic pathogens, without us even knowing it. Just because water looks, clear, cold and inviting, doesn’t mean it is. That water could be filled with bacteria that can kill you and the only way you’ll know is to take the risk and try drinking it.

That’s why water purification is such an important part of survival. Rather than take a risk, every bit of water that we drink needs to be purified; even if it comes from a clear mountain stream. There’s always the possibility that someone upstream of us has been using that stream as a latrine, not being considerate of the others who need to use it.

While there can be other things in the water, such as chemicals, the greatest risk is from these microscopic pathogens. So, water purification concentrates on eliminating or killing those. The likelihood of chemicals or radioactive contamination is much lower and removing those from the water is much more complicated as well. Fortunately for us, there are a wide range of options which we can use for purifying water.

Water purification breaks down into three general categories: filtration, chemical and heat. We’ll take a look at all three of these, as well as some specific items which can be used for purifying water.


Filtration is the most common means of water purification for personal use. It consists of passing the water through a porous filter, which catches anything larger than the size of the pores. While some filters, such as whole house filters are only intended to catch sediment in the water, there are other filters which are excellent at catching bacteria, removing it from the water.

Berkley Filter

The Berkley filter is probably the best water filter you can buy. It is a multi-stage cartridge filter, which includes activated charcoal. As such, it not only removes sediment and bacteria, but some chemicals as well. While expensive to buy, the design of the filters allows them to be used for much more water than cheaper filter systems. This brings the cost per gallon down to less than those lower cost filters.

Sawyer Filter

Sawyer takes a very different approach to water filtration than other companies do. Their filter is a hollow fiber membrane. It is rated for rejecting anything larger than 0.02 microns, which means that it will filter out just about any bacteria in existence, as well as some of the larger viruses. But the truly amazing thing about this filter is that it is back-flushable. That means that you can run some of the purified water back through the filter and clean it out. This feature makes the filter last virtually forever. In fact the company guarantees it for one million gallons of water.


The LifeStraw is probably about the best of a category of filters known as “straw filters.” The name comes from the idea that you can drink water through it, like a straw. As the water passes through the filter, it is purified. Originally invented for use in third-world countries, where water purification plants and running water are all but unheard of, the LifeStraw will filter 1,000 liters of water before needing replacement.


Another invention for use in third-world countries is the bio-filter. This is something you can make yourself out of naturally available materials. The filter itself consists of three layers:

  • Pea Gravel
  • Sand
  • Activated Carbon or Activated Charcoal

Ideally, the layers should be as thick as possible, especially the layer of activated carbon. Water poured into the filter goes through the pea gravel first, which removes large solids. It then goes through the sand to eliminate sediment. Finally, the water passes through the activated carbon, which catches bacteria, protozoa and absorbs some chemicals.

A bio-filter can be made in one five-gallon bucket, but it’s easier to make it in three stacked buckets. Holes will need to be made in the bottoms of the buckets and something placed there to keep the material from falling through to the next bucket. Twenty-five to fifty pounds of gravel and sand can be used in the top buckets, with 25 pounds of activated carbon in the bottom one. It is important to rinse all the materials, in order to remove the dirt and dust, so that the water will come out clean.


Chemical purification is used commonly for purification of municipal water supplies. Chlorine is added to the water, in order to kill all pathogens. The same is added to swimming pools for much the same reason. You can use this means yourself, but you will be limited in a survival situation to how much of the chemicals you have on hand.


Chlorine is readily available in any store that carries swimming pool supplies, but it is even easier to find as normal bleach used for whitening clothes. The advantage of using bleach is that it is already in a liquid form, making it easier to use for small quantities of water. Most of us don’t need to purify a swimming pool worth of water at one time.

To use bleach as a water purifier, you need the simple bleach, not the scented bleach or the color-safe one. Buy the cheap stuff and you’ll be in good shape. Add eight drops of water per gallon, mix and allow it to sit for about 30 – 60 minutes. It will finish killing all pathogens in that time.

If you are trying to purify larger quantities of water, such as a 55 gallon drum, you can measure the bleach in milliliters, rather than in drops. There are 20 drops per milliliter, so for a 55 gallon drum of water; you’d need 55 x 8 ÷ 20 milliliters. That equals 22 ml of bleach.

If the water is cloudy, make sure you filter the water first before adding the bleach.


Iodine works much like chlorine bleach and is very commonly used in third-world and emerging countries for water purification. The only problem with it is that it is more expensive than bleach is.

To use iodine, you’ll want a tincture of iodine. That’s iodine dissolved in alcohol. How much you use will depend on how murky the water is. For clear water, use 10 drops per gallon; for murky water, use 20. Mix it and allow it to sit, just like with the bleach.

Halazone Tablets

The military developed halazone tablets for water purification in the early 1900s. It was used extensively throughout the World War I and World War II. Chemically based on chlorine, it works in much the same way.

Typically, two of the tablets are used per quart of water, which is what a military canteen carries. They are good for an emergency, but rather expensive for long-term water purification. Besides, water purified in this manner tastes horrible.


The third method of purifying water, heat, is one of the most effective; however, it is one of the most time-consuming means of purification. When the temperature of the water is raised high enough, it kills the bacteria, protozoa and even viruses, making the water safe to drink.


It is common knowledge that boiling water will kill all pathogens in it. For this to work, it is necessary to bring the water to a boil and keep it at that temperature for five minutes. Typically, the water is than allowed to cool before use.

When cooking with water, such as making soups, pasta or rice, it is normal to bring the water to a boil. Therefore, it is not necessary to purify this water, before using it for cooking. Merely make sure that the water comes to a boil in the cooking process and it will be purified, as well as the food placed in it.


Louis Pasteur, a mid 1800s scientist was one of the first microbiologists. He discovered that it was not necessary to bring the water all the way up to 160 degrees in order to kill microscopic pathogens, but only to 158oF. This process is commonly used to purify milk and beer and is named after the inventor.

There are two big advantages of pasteurization. The first is that it doesn’t cook the food, like boiling will. That’s why it is used for milk. The second is that less energy has to be expended to heat the liquid being pasteurized. So, if firewood is scarce, this is a good energy saving method.

In order to pasteurize water as a means of purification, you’ll need a thermometer or a WAPI (water pasteurization indicator). The WAPI is another invention created for use in third-world countries. It consists of a plastic capsule with a wax bead in it. It is placed in the water, while the water is being heated. When the water reaches 160 degrees, the wax bead melts, dropping down in the capsule and indicating that the water is hot enough.

Solar Pasteurization

Just as the heat from a fire can be used to pasteurize water, so can heat created from the light of the sun. The easiest way to do this is to use empty clear soda bottles. Clean out the bottles and remove the labels. Then, fill them with water to be purified. Place the bottles horizontally in the sun, such as on top of a corrugated metal roof. A dark colored or metal surface helps, as it heats the water faster.

If you have a WAPI, it can be used in conjunction with solar pasteurization, just as it can for purifying water over a fire. If not, you’ll either need a thermometer or trust that several hours in the sun will get the water hot enough to pasteurize it.


Distillation is the surest way of purifying water. It is not only able to eliminate pathogens, but minerals (salts) and many chemicals as well. However, it requires constructing a still.

Basically, a still consists of a retort or metal container, with a top that will seal, such as a pressure cooker. A piece of copper tubing is attached to a hole in the lid of the retort and run off to one side, sloping downwards. In order to maintain the downward slope, it is common for the tube to be bent into a spiral. This is the condenser.

Water placed in the retort is heated by fire, causing it to turn into steam. That travels into the copper condenser, which causes it to cool and condensate inside the tube. The drops of water then travel down the tube and fall into a container as purified water.


Drinking water straight from the source is a risky business, but as you can see there are numerous ways in which you can make the water safe.

Have you used any of these methods in the wild? Which ones worked well for you? Let me know in the comments!


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Survivalist, woodsman, writer.

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