Emergency Preparedness/Disaster Services

514- How to Purify Water

In a disaster situation, water of uncertain quality should be purified before it is used for drinking, food preparation or hygiene. In addition to having a bad odor and taste, contaminated water can contain microorganisms that cause diseases such as dysentery, cholera, typhoid and hepatitis.

There are many ways to purify water, though none is perfect. Often the best solution is a combination of methods. Before purifying, let any suspended particles settle to the bottom, or strain them through layers of clean cloth. Following are four purification methods. The first three methods -- boiling, chlorination and purification tablets -- will kill microbes but will not remove other contaminants such as heavy metals, salts, most other chemicals and radioactive fallout. The final method, distillation, will remove microbes as well as other contaminants including radioactive fallout.

Boiling is the safest method of purifying water:

• Bring water to a rolling boil for 10 minutes, keeping in mind that some water will evaporate. Let the water cool before drinking.
• Boiled water will taste better if oxygen is replaced by pouring it back and forth between two containers. This will also improve the taste of stored water.

Chlorination uses liquid chlorine bleach to kill microorganisms:

• Use liquid bleach that contains 5-1/4% sodium hypo-chlorite and no soap. Some containers warn, "Not For Personal Use." You can disregard these warnings if the label states sodium hypo-chlorite as the only active ingredient and if you use only the small quantities mentioned in these instructions.
• Add two drops of bleach per quart of water (four drops if the water is cloudy), stir and let stand for 30 minutes. If the water does not taste and smell of chlorine at that point, add another dose and let stand another 15 minutes.
• If you do not have a dropper, use a spoon and a square-ended strip of paper or thin cloth about 1/4 inch by 2 inches. Put the strip in the spoon with an end hanging down about 1/2 inch below the scoop of the spoon. Place bleach in the spoon and carefully tip it. Drops the size of those from a medicine dropper will drip off the end of the strip.

Purification tablets release chlorine or iodine. They are inexpensive and available at most sporting goods stores and some drugstores. Follow the package directions. Usually one tablet is enough for one quart of water. Double the dose for cloudy water.

Distillation involves boiling water and then collecting the vapor that condenses back to water. The condensed vapor may include salt or other impurities:

• Fill a pot halfway with water.
• Tie a cup to the handle on the pot's lid so that the cup will hang right-side-up when the lid is upside-down (make sure the cup is not dangling into the water).
• Boil the water for 20 minutes. The water that drips from the lid into the cup is distilled and ready for use.