Instructions for Disinfecting Water Wells

Newly constructed, repaired, flooded, submerged or seasonal wells and wells which have tested positive for coliform bacteria need to be disinfected.  Water from such wells should not be used for drinking until proven safe by laboratory testing.

The water well and household water pipes may be disinfected using the following simple method:

1. Bypass or remove all water treatment devices before starting.
2. Run the faucet until the water is clear.  If it doesn't clear, call the Marquette County Health Department, Environmental Health Division, at (906) 475-4195.
3. Measure the well casing inside diameter and use the table below to determine the total amount of household bleach.  If the well is less than 50 feet deep, use the amount of bleach indicated but for deeper wells use additional amounts in proportion to the increased depth.  Use unscented common household bleach (active ingredient 5¼% sodium hypochlorite).

   For example, from the table below a 75 foot deep well with a 5 inch casing would require a total of ¾ gallon of bleach.

   Well Casing ID	Depth of Well	Bleach Required
   1¼ inch	50 feet	1/2 cup
   2 inch	50 feet	1 1/3 cups
   3 inch	50 feet	3 cups
   4 inch	50 feet	1 1/3 quarts
   5 inch	50 feet	1/2 gallon
   6 inch	50 feet	3/4 gallon

4. Shut the power to the pump off to avoid any possible electrical shock and remove the well cap.
5. Add the total bleach required to 5 gallons of water in a clean bucket and slowly pour the bleach and water mixture into the well.
6. Connect a garden hose to an outside faucet and position the hose inside the well casing.  Turn the pump on and flush for 10 to 15 minutes.  You should be able to smell bleach water coming out of the hose.
7. Open all cold water faucets in the home starting closest to the well, allow water to run until you smell bleach, and then turn off the faucets.
8. Open all hot water faucets one at a time, starting closest to the hot water tank, allow water to run until you smell bleach and then turn off the faucets.
9. Use no water for at least 4 hours; however, overnight is recommended.
10. To remove the bleach, attach a garden hose to an outside faucet and run the water onto the ground until you can no longer smell any bleach.   Do not run the water inside your home if connected to a septic system, as the large volume of water may damage the system.  Use caution not to run the water onto grass or other vegetation which may die as a result of the bleach water.  Open all faucets and run the water until you can no longer smell bleach.
11. Once you are convinced that there is no longer any bleach water in the system, you may collect a sample for coliform bacteria testing.   Sterile water sampling bottles are available at our office located across from the Marquette County Airport on U.S. Highway 41 East in Negaunee Township.
12. Collect the sample from a suitable tap located as close to the well as possible.  Do not collect the sample from softened or filtered water.
13. Don't forget to reverse the bypass or re-connect water treatment devices after you have collected the sample.
14. Failure to obtain a "not detected" laboratory result after disinfecting should be discussed with the Division of Environmental Health or a licensed well driller.  If the above method fails to produce a safe bacteriological sample, consider the possibility of a construction deficiency.  This may be particularly true when disinfecting an older well where the structural integrity of the system is unknown.

For more information on this subject, please contact:

Last UPdate:  03 February, 2005