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| Emergency Disinfection of Drinking Water  
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         EPA 810-F-93-002         July 1993      

         In times of extreme crisis, local health departments may urge         consumers to use more caution or to follow additional measures. If         local public health department information differs from this advice,         the local information should prevail.      

         When the home water supply is interrupted by natural or other forms of         disaster, you can obtain limited amounts of water by draining your hot         water tank or melting ice cubes. In most cases, well water is the         preferred source of drinking water. If it is not available and river         or lake water must be used, avoid sources containing floating material         and water with a dark color or an odor.      

         When emergency disinfection is necessary, examine the physical         condition of the water. Disinfectants are less effective in cloudy         water. Filter murky or colored water through clean cloths or allow it         to settle, and draw off the clean water for disinfection. Water         prepared for disinfection should be stored only in clean, tightly         covered, containers, not subject to corrosion.      

         There are two general methods by which small quantities of water can         be effectively disinfected. One method is boiling. It is the most         positive method by which water can be made bacterially safe to drink.         Another method is chemical treatment. If applied with care, certain         chemicals will make most water free from harmful or pathogenic         organisms.      
         METHODS OF EMERGENCY DISINFECTION      
**Boiling:** Vigorous boiling for one minute will kill any         disease-causing microorganisms present in water (at altitudes above         one mile, boil for three minutes). The flat taste of boiled water can         be improved by pouring it back and forth from one         container to another (called aeration), by allowing it to stand for         a few hours, or by adding a small pinch of salt for each quart of water         boiled.      

**Chemical treatment:** When boiling is not practical, chemical         disinfection should be used. The two chemicals commonly used are         chlorine and iodine. Chlorine and iodine are somewhat effective in         protecting against exposure to Giardia, but may not be effective in         controlling Cryptosporidium. Therefore, use iodine or chlorine only to         disinfect well water (as opposed to surface water sources such as         rivers, lakes, and springs), because well water is unlikely to contain         these disease causing organisms. Chlorine is generally more effective         than iodine in controlling Giardia, and both disinfectants work much         better in warmer water.      
         CHLORINE METHODS      
**Chlorine Bleach:** When boiling is not practical, chemical disinfection         should be used. Common household bleach contains a chlorine compound         that will disinfect water. The procedure to be followed is         usually written on the label. When the necessary procedure is not         given, find the percentage of available chlorine on the label and use         the information in the following tabulation as a guide.      
               Available Chlorine                           Drops per Quart of Clear Water            
                  1%               

                  10               

                  4-6%               

                  2               

                  7-10%               

                  1               

         (If strength is unknown, add ten drops per quart of water. Double         amount of chlorine for cloudy or colored water or water that is extremely         	cold.)      

         The treated water should be mixed thoroughly and allowed to stand, preferably         	covered, for 30 minutes. The water should have a slight chlorine odor;         	if not,         repeat the dosage and allow the water to stand for an additional 15         minutes. If the treated water has too strong a chlorine taste, it can         be made more pleasing by allowing the water to stand exposed to the         air for a few hours or by pouring it from one clean container to         another several times.      

**Granular Calcium Hypochlorite.** Add and dissolve one heaping         teaspoon of high-test granular calcium hypochlorite (approximately 1/4         ounce) for each two gallons of water. The mixture will produce a stock         chlorine solution of approximately 500 mg/L, since the calcium         hypochlorite has an available chlorine equal to 70 percent of its         weight. To disinfect water, add the chlorine solution in the ratio of         one part of chlorine solution to each 100 parts of water to be         treated. This is roughly equal to adding 1 pint (16 oz.) of stock         chlorine to each 12.5 gallons of water to be disinfected. To remove         any objectionable chlorine odor, aerate the water as described above.      

**Chlorine Tablets.**Chlorine tablets containing the necessary         dosage for drinking water disinfection can be purchased in a         commercially prepared form. These tablets are available from drug and         sporting goods stores and should be used as stated in the         instructions. When instructions are not available, use one tablet for         each quart of water to be purified.      

**TINCTURE OF IODINE**

         Common household iodine from the medicine chest or first aid kit may         be used to disinfect water. Add five drops of 2 percent United States         Pharmacopeia (U.S.P.) Tincture of iodine to each quart of clear water.         For cloudy water add ten drops and let the solution stand for at least         30 minutes.      

**IODINE TABLETS**

         Commercially prepared iodine tablets containing the necessary dosage         for drinking water disinfection can be purchased at drug and sporting         goods stores. They should be used as stated. When instructions are not         available, use one tablet for each quart of water to be purified.      

**WATER TO BE USED FOR DRINKING, COOKING, MAKING ANY PREPARED DRINK,         OR BRUSHING THE TEETH SHOULD BE PROPERLY DISINFECTED.** |
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