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Disinfection of Wells and Small Distribution Systems

Wells that are contaminated with coliform bacteria should not be used for potable purposes until they have been adequately disinfected and retested to verify that they are free of contamination.

(Please read all the instructions before proceeding.)

1) During this procedure the water will not be drinkable so plan to do it late at night or at other times when there is little need for water. Obtain one-half gallon of fresh household bleach (unscented) which contains 5-6% sodium hypochlorite. Large diameter or very deep wells may require more chlorine. Dilute the chlorine in a large bucket of water.

2) Remove the sanitary seal and pour the chlorine solution down the well casing. Using a clean hose, run water down the casing until you smell chlorine in the water from the hose. Turn off the hose and replace the sanitary seal.

3) Open each tap in the distribution system until you smell the chlorine, then close the tap. The goal is to get the chlorine solution to all parts of the plumbing. Do the same for hot water taps and flush toilets until chlorinated. If there are any in-line filters, they should be removed, and replaced with new filters after the disinfection is completed. (Carbon filters are notorious for breeding bacteria.)

4) Hold the chlorine in the pipes a minimum of two (2) hours, preferably overnight.

5) Open all taps and flush out the chlorine solution until you can no longer smell it at any of the taps. Your well and distribution system should now be disinfected.

6) Follow-up sampling should be done after all trace of chlorine is gone to ensure that the disinfection procedure was successful. DEC Drinking Water personnel will advise public water suppliers of their sampling requirements.

NOTE: Large amounts of chlorine can damage the resin in water softeners, so if there is a softener, it should be by-passed before disinfecting the plumbing. Contact the manufacturer or distributor for the correct method for disinfecting the softener.

For More Information, Contact the Alaska Department of Environmental Conservation Drinking Water Program at:

Anchorage: (907) 269-7656 Fax (907) 269-7655
Fairbanks: (907) 451-2108 Fax (907) 451-2188
Kenai: (907) 262-5210 Fax (907) 262-2294
Mat-Su: (907) 376-1850 Fax (907) 376-2382

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