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Survival Water Purification
Methods of disinfecting water during an emergency situation and in the wilderness

Water, apart from shelter, can become the most immediate need in a survival situation. Depending on the level of activity, and ambient temperature, a person can live about 3 days without water. Prolonged activity without proper hydration coupled with malnutrition will quickly lower our chances for survival.

The first problem is finding water, depending on the location this may prove more difficult than ensuring it's potability. However, for the scope of this article, we will assume that a source has already been located.

You do not want to wait until you are thirsty to begin gathering water, as the urge to drink directly from the contaminated source can become unbearable. Due to the negative effects of drinking water contaminated with Giardia and other bacteria/viruses, this is a bad idea. Becoming sick from drinking bad water, will further dehydrate you, worsening your situation.

Having some knowledge of the type of contaminants we could deal with is important. When choosing a ceramic filter it is a good idea to get information on the filter's micron rating:

Some contaminants and their size in microns:

Contaminant size
Contaminant Size
Giardia lamblia 8 to 12 microns
Cryptosporidium parvum 4 to 6 microns
Bacteria (salmonella - E.coli 0.2 to 4 microns
Viruses 0.004 to 0.1 microns

Water carrying:

In the most ideal situation you will have a solid container to carry the water that you find (i.e. metal/plastic pot, water bottle, milk jug, canteen). However, other alternatives to consider are:

a plastic sheet, folded to form a bag
a condom, preferably with no spermicide, or lubricant, inside of a sock to prevent bursting the latex

Some canteens have a built-in screen to help block large particles. Heavier sediment will make it more difficult to purify the water from contaminants. Another good idea is to use anything from a coffee filter to a piece of cloth to pre-filter the water. This collapsible canteen from the military has a screen that will catch the larger particles.

Running water is usually best but if the water is from a still source try to find a place where the heavy sediment has settled.

Water filtration:

As long as the water has been purified properly, filtration is mostly to make the water more attractive. Since most of us aren't used to, drinking water with, leaves, algae, dirt, etcetera. So, at least a minimal amount of filtration is recommended. Since, while you can ingest/digest the aforementioned, most of us would prefer not to.

The simplest levels of filtration can be achieved by running the water through a cloth. The tighter the weave of the cloth the better it will filter water, as it will be able to capture smaller/finer particles. Just about any cloth will catch the “big” stuff. Folding the cloth to form multiple layers will help in this process.

If you are setting up a long term camp, you can set up a more intricate filtration system, that will not only filter particulates, but also improve taste.

Water purification:

Most water purification techniques are fairly simple. Below are the most common methods of purifying water.


Boiling is the simplest method of killing bacteria/viruses. The concept is, that the organism is destroyed by pushing the bacterium/virus past it's heat range. 100*C(212*F) will effectively kill most organisms, not just bacteria.

Assuming you can get a fire going, and have a metal container. After filtering as many of the particulates as possible. Fill your container with water, place over the fire, bring to a rapid boil, then allow to cool (drinking hot water can induce vomiting). Boiling will kill the harmful bacteria in the water, as they cannot withstand the temperature.

Advantage is that you are not adding any chemicals to your water, which takes out the guess work as far as dosage. The disadvantage, if it can even be called that, is that you have to have a source of heat(fire, stove, etc.) in order to bring the water to the boiling point.

Water purification through chemical treatment

Common chemicals used:

* Iodine
      * tablets
      * crystals
      * tincture of iodine
* Sodium Chlorite / Chlorine Dioxide
* Potassium Permanganate
* Chlor-floc

Some parasites may not be killed using this method.

Purification capability can be reduced by several factors:

* Temperature of the water
* Clarity of water
* Tablet expiration date

Treating with iodine crystals

Iodine solutions kill bacteria by upsetting the ion balance within the cell, replacing chemicals that the bacteria needs to survive with iodide ions. Iodine can also be poisonous to humans, and can be especially harmful to young children, and pregnant women. You should be careful not to use too much iodine when purifying your water, and if at all possible avoid using it as a primary purification method for extended periods of time. If you find yourself in a survival situation, for an extended period of time, you should consider setting up a still, or boiling the water if possible.

Simply fill the provided container with water. Shake the container. Allow the filled container to stand for about an hour. This allows time for the water to become saturated with iodine. Add the iodine to your water container, adding the indicated amount of capfuls (it's about 1 capful to 1 quart). Shake the water container to ensure a proper mixture. Allow the container to sit 20-30 minutes. Afterwards the water is ready to drink.

Iodine tastes just like it smells, fortunately, this is a pretty weak solution, so the taste is not overpowering; it is only slightly worse than city water. The advantages of iodine crystals, is that, one container can treat somewhere in the neighborhood of 10,000 gallons. As well as the fact that, it prepares the water relatively fast. The disadvantage is, as mentioned above, that it is harmful in the long term.

Note: Using this method on water from a running stream, proved to have no ill effects on my digestive system.

Treating with iodine tablets

Sodium Chlorite / Chlorine Dioxide tablets

These tablets essentially use chlorination as their method of purification. Sodium chlorite generate chlorine dioxide giving it the ability to treat water. Chlorination, as most know, is a common method of disinfecting water, and is commonly used by municipalities world-wide for this purpose. Chlorine destroys bacteria by destroying the cell walls of the bacterium/virus, killing the organism. Fortunately, when we drink chlorinated water, our digestive system quickly neutralizes the chlorine. So chlorine concentrations along the gastrointestinal tract are, in all likelihood, too low to cause damage.

Add one of these tablets to a quart of water. Allow it to sit for approximately 4 hours. Personally, I feel that shaking the container once or twice helps dissolve the tablet more quickly, and improve distribution of the tablet.

Water treated in this manner has a slight bleach/chlorine taste, which is less potent than your average city water. The advantage of these pills is their simplicity; add the tab, and let sit. The disadvantage is that you will be waiting for a while before you can drink it.

Note: Using this method on water from a running stream, proved to have no ill effects on my digestive system.

Potassium Permanganate - ( Condy's Crystals or KMNO4 ) can be purchased at hardware stores. Sold as a water softener. Can be purchased in both powder and pill form (permitabs). This chemical compound has many uses from fire starting to water purification. Just a few crystals can treat a quart of water.

( aproximately 0.01% solution) 1 gram per liter (3 - 4 crystals)

Micro-filtration/Water Filters

Micro-filters such as the one pictured below remove contaminants from the water using a ceramic filter. By passing the fluid through the microporous membrane with pore sizes smaller than the contaminant we effectively remove pathogens.

Survival Filter Straws

There are several manufacturers of survival straws or emergency water filter systems. This one is from Aquamira.

Information from Aquamira: "One unit will filter up to 20 gallons (75L) of water. Tests indicate that the Frontier Filter will remove 99.9% of Cryptosporidium and Giardia. The Frontier Emergency Water Filter System is also easy to operate, just attach and expand the straw, submerge the filter end into the water source, and drink through the straw."


Please see our Solar Still article.

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Other chemicals can be used in case of an emergency such as:

Iodine tincture - Around eight drops per liter or about thirty per gallon
EPA suggestions: You can use tincture of iodine to disinfect filtered and settled water.
Common household iodine from the medicine chest or first aid kit may be used to disinfect water. Add five drops of 2 percent U.S. or your country’s approved Pharmacopeia tincture of iodine to each quart or liter of clear water. For cloudy water add ten drops and let the solution stand for at least 30 minutes.

Bleach - Two drops of bleach per quart 1/8 teaspoon (or eight drops) of regular, unscented, liquid household bleach for each gallon of water

Hydrogen peroxide - (untested) During research we found recommended thirty-five to fifty percent concentration being used.

Less common methods used in an emergency are covered in the article below:

Emergency Water Filtration

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Transpiration / Perspiration / Vegetation Bags

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Solar Still

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