In Emergency, Disinfect Drinking Water by Boiling or Chemical Treatment

June 27, 2008

Iowans dealing with unsafe drinking water have two options for disinfecting small quantities of water, says Sam Beattie, food science and safety specialist with Iowa State University Extension.

“You can boil the water or you can chemically treat it. In either case, be careful.” Beattie cautioned.

Boiling is the most positive method by which water can be made bacteriologically safe to drink, he said. Certain chemicals, if applied with care, will make most waters free of harmful or pathogenic organisms.

“The bacteria, viruses and parasites that were contained in the floodwaters are likely to have contaminated many wells. These illness-causing organisms survive in water for a long time and need to be killed,” Beattie said.

“Boiling water is the preferred disinfection method, especially for people whose immune systems are compromised,” he added.

Disinfect water to be used for drinking, any type of prepared drink, ice, cooking, washing cuts, brushing teeth and rinsing clean dishes.

Store clean, disinfected water in a sanitized container. Use 200 ppm of chlorine bleach to disinfect dishes and water storage vessels. If the container is threaded, make sure to sanitize the lid and threads, he said.

Where do you get the water?
When the water supply to a home is interrupted by natural or other disasters, limited amounts of potable water may be obtained by melting ice cubes, Beattie said. Water from the hot water tank can be used, but may have higher mineral concentrations and would be more suitable for washing plates and utensils.

“Do not use water from the toilet tank for drinking. It is likely to be contaminated,” Beattie said.

Generally, groundwater is the preferred source of drinking water, he continued. If it is not available and surface water must be used, avoid sources that contain floating material or have a dark color and/or odor.

People with rural wells should boil their water if the safety of their well water is questionable, he added.

When emergency disinfection is necessary, consider the water’s physical condition, Beattie continued. “Cloudy water is harder to disinfect and you won’t be able to disinfect it to the same degree as clear water.”

Filter murky or colored water through clean cloths or allow particles to settle. Beattie recommended. “Then draw off or decant the water, from the top, that you will disinfect. Store water that you’ve prepared for disinfection in clean, tightly covered containers that will not corrode.”

Boiling water for emergency disinfection
Boil water at a rolling boil for one minute. This will kill any disease-causing microorganisms present in the water.

“You can improve the flat taste of boiled water by pouring it back and forth from one clean container into another (this is called aeration), by allowing it to stand for a few hours or by adding a pinch of salt for each quart of water boiled,” Beattie said.

Chemical treatment for emergency disinfection
When boiling water is not practical, chemical disinfection can be used, Beattie noted. The two most common chemicals are chlorine and iodine. These chemicals are available in various forms.

Chlorine Bleach. Common household bleach contains a chlorine compound that disinfects water. Usually the procedure to follow is written on the label. If it is not, find the percentage of available chlorine on the label and use the following dosages as a guide. (See Table1.pdf, Available Chlorine in Household Bleach for Use as Water Disinfectant.) Do not use bleach with scented or color-safe additives or bleaches containing soaps.

Mix thoroughly and allow the treated water to stand for 30 minutes. The water should have a slight chlorine odor; if it does not, repeat the dosage and allow it to stand for another 15 minutes. If the treated water has too strong a chlorine taste, it can be made more palatable by allowing the water to stand exposed to the air for a few hours or aerate using the method described above.

Granular Calcium Hypochlorite. Add and dissolve one heaping teaspoon of high-test calcium hypochlorite (approximately 1/4 ounce) for each two gallons of water. This mixture produces a stock chlorine solution. To disinfect water, add the stock chlorine solution in a ratio of one part chlorine solution to 100 parts of water to be treated. This is roughly equal to adding 1 1/4 ounce of stock solution to each gallon of water. To remove any objectionable chlorine odor, aerate the water as previously described.

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.

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 10 drops and let the solution stand for 30 minutes.

Iodine Tablets. Commercially prepared iodine tablets containing the necessary dosage for disinfecting drinking water can be purchased at drug and sporting goods stores. Use as stated in the instructions. When instructions are not available, use one tablet for each quart of water to be disinfected.

Contacts :
Sam Beattie, Food Science/Human Nutrition, (515) 294-3357, beatties@iastate.edu
Laura Sternweis, Extension Communications and External Relations, (515) 294-0775, lsternwe@iastate.edu

Table1.pdf Available Chlorine in Household Bleach for Use as Water Disinfectant