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Emergency Disinfection of Drinking Water
Posted on Monday July 08, 2019
In the event of an emergency situation where regular water service has been interrupted your water may need to be disinfected.

Emergency Disinfection of Drinking Water

In an emergency situation where regular water service has been interrupted - floods, water service interruptions, or contamination events - the department and the local public water system may recommend using only bottled water, boiled water, or for homeowners to disinfect the water until regular water service is restored.

The instructions below, compiled from several Missouri Department of Natural Resources fact sheets and EPA guidance documents, show you how to boil and/or disinfect water to kill most disease-causing microorganisms that may be present in the water. The disinfection methods listed below describe the minimum treatment required to make your water safe to drink and are the recommended procedures in communities where "boil orders" or "boil advisories" have been issued. If the water is cloudy or contains particles of foreign material, the recommended chlorine dosage should be doubled.

Please Note: boiling or disinfection will not destroy other contaminants such as chemicals, heavy metals or salts and is not appropriate when a "Do Not Drink Order" or a "Do Not Use Order" has been issued. Freezing does not disinfect water. Freezing will not kill bacteriological contaminants in drinking water. Discard all ice cubes if a boil water notice is issued.


Boil Water:

Boiling is the most effective method for killing disease-causing organisms in the water including microorganisms like Giardia lamblia and Cryptosporidium, which are frequently found in rivers and lakes.

  1.  If the water is cloudy, strain the water through a clean, tightly woven cloth into a clean container to remove any sediment or foreign material,
  2. Boil the water at a rolling boil for at least one full minute up to three minutes.
  3. Allow the water to cool. When it is cool, it is ready for use.
  4. To improve the flat taste of boiled water a pinch of salt can be added to each quart of boiled water, or pour water back and forth from one clean container into another several times.

Disinfecting water using household bleach:

If you can't boil water, the water can be disinfected using laundry bleach or iodine. Only use regular, unscented. chlorine bleach products that are suitable for disinfection and sanitation as indicated on the label. Do not use scented, color safe, or bleaches with added cleaners.

  • If water is cloudy, let it settle and filter it through a clean cloth, paper towel, or coffee filter.
  • Locate a clean dropper from your medicine cabinet or emergency supply kit.
  • Locate a fresh liquid chlorine bleach or liquid chlorine bleach that is stored at room temperatures for less than one year. Check the label to determine the percent of available chlorine, and follow the instructions below.
  • Use the table below as a guide to decide the amount of bleach you should add to the water, for example, add 10-12 drops of bleach to each gallon of water. Double the amount of bleach if the water is cloudy, colored, or very cold.
  • Mix thoroughly by stirring or shaking the water in its container. Let the treated water stand for 30 minutes.
  • The water should have a slight chlorine odor. If it doesn't, repeat the dosage and let stand for another 15 minutes before use.
  • If the chlorine taste is too strong, pour the water from one clean container to another and let it stand for a few hours before use.

     Available Chlorine*
     Drops per Quart or Liter**
     Drops per Gallon**
     4% to 6%
     2  8-10 drops (1/8 Teaspoon)
     8% to 10%
     1  6 drops
    *If strength is unknown, add 10 drops per quart or liter of water.
    **Double the amount for cloudy or colored water.

Iodine (USP Tincture of Iodine)

  1. Make sure that nobody who will be drinking the treated water is allergic to iodine.

     Amount of Water Disinfected
     Amount of Iodine
     1 Gallon
     10 to 12 drops (about 1/8 teaspoon)
     5 Gallons
     1 teaspoon
     10 Gallons
     2 teaspoons

  2. Mix thoroughly by stirring or shaking water in its container. Let the treated water stand for 30 minutes.

Other Disinfection Methods

Granular calcium hypochlorite. High-test granular calcium hypochlorite, known as HTH and other brand names, has 70% available chlorines. The first step is to make a chlorine solution that you will use to disinfect your water. For your safety, do it in a ventilated area and wear eye protection. Add one heaping teaspoon (approximately ¼ ounce) of high-test granular calcium hypochlorite (HTH) to two gallons of water and stir until the particles have dissolved. The mixture will produce a chlorine solution of approximately 500 milligrams per liter. To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating. This is about the same as adding 1 pint (16 ounces) of the chlorine solution to 12.5 gallons of water. If the chlorine taste is too strong, pour the water from one clean container to another and let it stand for a few hours before use. CAUTION: HTH is a very powerful oxidant. Follow the instructions on the label for safe handling and storage of this chemical.


Flushing Home Water Lines

After a flood or a water system contamination event, you may need to flush the home's internal plumbing.

  1. The best and easiest way to begin flushing your water lines is to turn on one or two outside garden faucets and let the water run for half an hour. You can use this to wash off the exterior of the house or the driveway and sidewalks. This will avoid overloading the public sewer system, or your septic system, by flushing all of the water down the household drains.
  2. Water pipes in your home that have been submerged in flood water may be extremely dirty. Clean the exterior of pipes and faucets with regular household cleaner. Remove any aerators (screens) and clean them, then briefly turn on hot and cold water at all faucets to remove dirt that may have settled just inside the faucets.
  3. Next, squirt a solution of 50 percent water and 50 percent household bleach into the faucets. Then flush all water pipes as described in Step 4. Never mix bleach with a household cleaner containing ammonia. The mixture can create a deadly chlorine gas.
  4. Sequentially flush out all water pipes inside the house. Begin at the faucet nearest the point where the waterline enters the building. This is usually the sink nearest the water meter. Turn on both hot and cold faucets at full blast for three to five minutes. Do not use water until it becomes clear. You may wish to catch water in buckets if you are concerned about overloading your septic tank. Proceed to the next nearest faucet and repeat. Continue until all faucets have been flushed. To avoid wasting hot water, wait until you have flushed all your lines to turn on your hot water heater.
  5. Your tap water should now be safe to drink, and you can replace the faucet aerators.


If You Have a Private Well

Wells that have been affected by flood waters or have bacteriological contamination should be disinfected prior to being used for drinking water. Homeowners should follow the procedures listed in the department's publication "Well and Water System Disinfection for Public Drinking Water Systems" available on the department's website under the Public Drinking Water tab.

If muddy water is present, contact a permitted well driller for use and start-up procedures. A list of permitted drillers is available from the department's Wellhead Protection section at 573- 368-2165.

Wells that are destroyed, totally filled with mud or suffered extensive damage must be plugged because they may cause further damage to the groundwater supply. If you want to have the same well re-drilled, you will need to contact a permitted well driller. Wells that are partially damaged or partially filled with mud can be cleaned out by a permitted pump installer or driller. They can also determine if other repairs are necessary. 


For More Information

Missouri Department of Natural Resources
Public Drinking Water Branch
PO Box 176
Jefferon City, MO 65102-0176
800-361-4827 or 573-751-5331


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