What is the procedure for disinfecting a well ? is a dug / shallow well different than a drilled well?

How much bleach to use and what dilute?

Well is 138 feet from top of casing, 128.76 Gal of water in well, pump is 10 feet from bottom of well and water is 50 feet from top of casing. Put in 1998, stopped use 2004.


1) Use common household bleach as the chlorine source for disinfection.

[Bleach products usually contain 5 to 6 percent chlorine. For the disinfection procedure to be effective, the pH (acidity) of the well water should be between 6 to 7.5. If it is not in this range, then a well treatment professional experienced in disinfection of high pH water should be consulted to adjust the pH and maintain it in the correct range during the disinfection process.

2) Find the total depth of water in the well.

[For example - If the well is drilled to 200 feet and the water level is 50 feet down from the top, then there is a 150 feet depth of water in the well]

3) Determine how many gallons of water are stored in the vertical column of the well. Once you know depth you can work out the gallons. (See Table 1 for specific Water Volumes)

Well diameter gallons per foot of well gallons in 100 feet

4-inch 0.65 65

6-inch 1.47 147

8-inch 2.61 261

[NOTE - disinfection is not feasible for large-diameter dug wells]

4) Work out how much bleach will be needed: For every 50 gallons of water in the well use one quart of laundry bleach - (4 quarts in a gallon). Do not use excessive amounts of bleach - more is not more effective.

[In most cases, one gallon of bleach will disinfect 200 gallons of well water at a chlorine concentration between 200 to 300 ppm (parts per million)]

[NOTE - Bleach loses strength in its container over time, Check the “sell by date” and use bleach that is less than three months old. Use unscented bleach to avoid adding unneeded chemicals to the water (It is usually less expensive too)]

5) For best results the bleach should be combined with water before adding it to the well.

[By reducing the concentration there is less chance of corrosion of the cables and pipes in the well. The greater volume of water helps get the chlorine mixed in the well column.]

[NOTE: - Do not mix chlorine solutions with other cleaning products, including ammonia, because toxic gases will be created.

6) Make the Chlorine-Water Mixture by filling a five gallon bucket with water and adding about one quart of bleach. Pour the mixture into the well and repeat until the right amount of bleach has been added to the well (see #4 above).

7) Remove the well cap and pour the mixture directly down inside the well casing.

[NOTE - Wear rubber gloves and safety glasses to protect skin and eyes from splashes. Spills contacting the body should be rinsed immediately and thoroughly with fresh water.]

8) Recirculate the water in the well by running water with a hose back into the well for 30 minutes.

[This will help draw the Chlorine-Water Mixture down the well and will wash the “dry” portion of the well casing or drilled hole above the water table more thoroughly.]

9) To disinfect the household plumbing first turn off the electric or gas supply to the hot water heater. Turn on all the faucets, shower heads, clothes washers, dish washers and outside faucets, etc. until there is a chlorine smell at each location.

[NOTE - If you have water conditioning equipment check the owners manual to see if it is sensitive to chlorination. All equipment in the water system should be disinfected because it may serve as a safe haven from which the bacteria may reinfect the system.]

10) Leave the Chlorine-Water Mixture in the plumbing system and well for 12 to 24 hours before removing the chlorinated water.

[NOTE - During the disinfection process, the well water should not be used for consumption, so make plans for essential water needs before you begin the disinfection process!]

11) Remove the chlorinated water from the well by running the pump and leading a hose from outside faucets to a safe area.

[Don’t put the chlorine solution into a septic system or in a creek or pond where it may kill fish. Flowers and vegetables may be affected by chlorinated water.]

12) When the chlorine odor has gone the well flushing is complete.

[If you have difficulty smelling the chlorine odor a swimming pool chlorine test kit can indicate whether or not there is chlorine remaining in the well water.]

13) Once the chlorine has been removed from the well water, the indoor plumbing may be flushed out to the septic or sewer system to remove the chlorinated water.

[Re-energize the hot water heater. The water supply should now be bacteria free.]

14) Wait about 5 to 10 days before resampling the water supply and testing for bacteria.

[If bacteria are still present, repeat the process. It may take several treatments to remove long-established bacteria colonies. If the problem persists, contact a professional familiar with microbiological contamination in wells.]

15) Repeat testing in three months to confirm treatment success, and then test annually.


  • 1
    If you are trying to stop a hydrogen sulfide ( rotten egg) smell; The problem is likely sulfate reducing bacterial living in the aquifer. I found that bleach was only a temporary fix in my 200 ft well in northern IL. The bleach killed bacteria near the well bore but the smell was back in less than a week. – blacksmith37 Apr 30 '19 at 21:18

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