How to Purify Water

Although many devices exist for making water safe to drink, you're probably not going to have one when you find yourself in a survival situation. So as a backup, here's a list of techniques you can use to improve the safety of the water you obtain in the wilderness. This article covers four different tactics: filtration, boiling, chemical treatment, and distillate.

Water Filtration
You'll need a filter. Either one that is pre-made such as those used by coffee makers or makeshift ones such as paper towels, writing paper, or tightly woven clothing. If you happen to have the right supplies, you can make a filter with a sock filled with crushed charcoal, small crushed rocks, and sand.

Whatever filter you use, be sure to pour the water through it several times. Also note that filtration removes impurities from the water and does nothing to kill bacteria and micro-organisms.

Boiling Water
Most of us know that boiling water will make it safer to drink. If you can, once you're done filtering the water (see above), consider boiling it too. The longer the boil the better up until the 10 minute mark after which there shouldn't be anything left alive in the water.

Chemical Treatment for Water
There are two common techniques for chemically treating water. The first is to use two drops of household bleach for each quart and the second is to us one iodine tablet (5 drops of drugstore iodine) per quart.

Regardless of the chemical used, let the water site for at least 1 hour. Ideally, let the water sit overnight to ensure that all microorganisms are killed. Be prepared for a funny flavor when you drink this water!

Distillation
In the wild you can use the power of the sun to distill water. The process is slow and the yield is small, but the water is as pure as you can get it.

  1. To build a still, start by digging a hole that is about a foot deep and as wide as whatever container you plan to use.
  2. Place the container (make sure it's clean) at the center of the hole and then cover the hole with a piece of plastic (e.g. tarp, garbage bag).
  3. Use sticks or stones to keep the plastic flush with the ground and to prevent air from escaping from the hole.
  4. Poke a hole in the center of the plastic and then place a rock next to the hole so that the plastic forms a funnel.
  5. As the day progresses, the heat of the sun will cause water from the ground to evaporate. This water will condense on the plastic and because of the funnel shape it will then drip in to the container. All you need to do at this point is wait.

Boiling water and chemical treatment achieve the same goal, but you should consider filtering the water as well. Distillation is as effective as filtration and boiling/chemical treatment so it's the ideal technique.

References:
The Worst Case Scenario Survival Handbook - Travel by Joshua Piven and David Borgenicht

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3 Comments

  1. i read a magazine and it said if you boil something for 10 minutites it kills everything in it. When water is boiled it usually kills most things.

  2. Chris Needham

    Scott, Will anything survive after it starts to boil? Probably not. In fact, boiling is really just a good visual indicator and everything in the water has already been killed before it actually starts boiling. If you had a thermometer you could stop before hitting a boil. Boiling times you see (from 1 minute recommended by the CDC, 10 minutes above, to 20 minutes you'll see elsewhere) are, in my opinion, attempts to make sure that no matter what your interpretation of "boiling" is, you will end up with bacteria-free water.

  3. Question: I'm pretty sure I read in Backpacker magazine that it was only neccessary to bring the water to a boil to kill everything in it, yet above you're saying up to 10 minutes. Is there any hard science you can point to for a concrete time? I've been wondering about this forever and don't know who to believe. I even wrote the Mythbusters about it...

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