From RedCross.org
In addition to having a bad odor and taste, water from questionable sources may be contaminated by a variety of microorganisms, including bacteria and parasites that cause diseases such as dysentery, cholera, typhoid and hepatitis. All water of uncertain purity should be treated before use.
To treat water for consumption and/or hygiene, follow these steps:
- Filter the water using a piece of cloth or coffee filter to remove solid particles.
- Bring it to a rolling boil for about one full minute.
- Let it cool at least 30 minutes. Water must be cool or the chlorine treatment described below will be useless.
- Add 16 drops of liquid chlorine bleach per gallon of water, or 8 drops per 2-liter bottle of water. Stir to mix. Sodium hypochlorite of the concentration of 5.25% to 6% should be the only active ingredient in the bleach. There should not be any added soap or fragrances. A major bleach manufacturer has also added Sodium Hydroxide as an active ingredient, which they state does not pose a health risk for water treatment.
- Let stand 30 minutes.
- If it smells of chlorine. You can use it. If it does not smell of chlorine, add 16 more drops of chlorine bleach per gallon of water (or 8 drops per 2-liter bottle of water), let stand 30 minutes, and smell it again. If it smells of chlorine, you can use it. If it does not smell of chlorine, discard it and find another source of water.
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Source: http://www.redcross.org/prepare/disaster/water-safety/water-treatment
