Make Potable Water In An Emergency

If, during an emergency, you only have access to untreated water, in most cases your main interest should be disinfecting it—killing the germs. But if toxic chemicals are a problem, things become more complicated. For example, if you’re drawing water from a stream that’s contaminated with factory runoff, disinfection won’t get rid of the chemicals. For that you need to distill the water (see page 244) or use charcoal filtration (see page 244). Even then, though, there’s no guarantee that all chemicals will be removed. (You also need to know these six proven skills to get you through any emergency.)

How to Disinfect Water

No matter which disinfection method you use, if the water is cloudy, first strain it through a clean piece of cotton fabric or a coffee filter. This removes debris and some bacteria. Then let the water sit for a couple of hours to allow residual sediment to settle. Pour all but the sediment into a clean container.


Bringing water to a rolling boil should kill all the germs in it, but by letting it boil for a minute or two you can be sure the water’s disinfected. Use a lid if you have it to keep the water as hot as possible and to keep some of that precious resource from evaporating away. (Know how to manage these everyday emergencies—Like when the power goes out or your gutters are overflowing.)


Chlorine kills viruses and bacteria, but it may not kill all the parasites, such as giardia and cryptosporidium—they’re carried in some animal feces, which often contaminates streams and lakes.

Add two to four drops of unscented 5.25-percent chlorine bleach (such as regular-strength Clorox) to each quart or liter of water. That’s eight to sixteen drops per gallon. Mix it well. Wait thirty minutes or so before drinking it.

If you’re using calcium hypochlorite granules (often used to disinfect swimming pools), it’s a two-step process. First mix your starter: one teaspoon of the granules dissolved in two gallons of water. Store this starter solution and label it “bleach—NOT FOR DRINKING.” It should stay good for about two weeks. Next add one part of this bleach solution to one hundred parts water. That equals:

  • Two teaspoons of bleach solution to one quart or liter of water
  • Eight teaspoons of bleach solution to one gallon of water
  • One pint of bleach solution to twelve and a half gallons of water

Mix well and let sit for thirty minutes before drinking. (Learn these emergency phrases before you travel to a foreign country.)


Don’t disinfect with iodine if anyone who will be using the water is allergic to it. Also, like chlorine, iodine may not kill all parasites.

Add one of any of the following items to each quart of water (for a gallon of water, multiply the quantities by four):

  • 1 iodine tablet
  • 5–10 drops 2-percent iodine solution
  • 8–16 drops 10-percent povidone-iodine (Betadine) solution
  • 1–2 small povidone-iodine (Betadine) pads

Mix well and let sit at least thirty minutes before drinking.


UV Rays from the Sun

To disinfect water using the sun’s ultraviolet rays, first ensure that the UV rays can get to all the germs: the water should be at least clear enough to read a newspaper through. If it’s not that clear even after filtering (see page 241), mixing a quarter teaspoon of salt into every quart or liter of water can help. But be aware that this is about six hundred milligrams of sodium and could overload someone on a salt-restricted diet. A typical low-sodium diet usually includes no more than two thousand milligrams per day. Some people should consume even less.

Then disinfect: put the water into a clear plastic bag, mason jar, or plastic bottle that holds no more than two liters. Seal the container, and place it on its side in the direct sun for six hours—forty-eight hours if the sky is really cloudy. Adding about a quarter teaspoon of 3-percent hydrogen peroxide or about an ounce of lemon or lime juice per liter of water can shorten the time the UV rays take to kill the bacteria.


Backpackers and hikers often travel with a portable microfilter that allows them to remove microscopic organisms from their drinking water. I recommend keeping a microfilter on hand for emergencies. When choosing one of these devices, make sure the manufacturer guarantees that it has no pores (holes) larger than one micron. Microfiltration is better than chemicals at removing parasites, but since viruses can be smaller than one micron, they might get through. So combining this method with the chlorine or iodine method described above is ideal. However, many filtration systems do come with a layer of activated charcoal, which will catch a lot of the escaped viruses.

Getting the water through the microfilter will require gravity or some other force, such as sucking the water through a special filtered straw. All microfilters should come with directions.

This is how you can test if your tap water is safe to drink.

08-concussion-survival-handbook-bookThe Survival Doctor’s Complete Handbook will take you step by step through the essentials of medical care during an emergency. Maybe you live alone in a rural area, or you just want to make sure you and your family are prepared to safely weather the next natural disaster. Whatever your situation and your health needs, The Squrvival Doctor’s Complete Handbook is your must-have medical resource.