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Well Chlorination

Ohio Department of Health - Bureau of Environmental Health

Disinfection Fact Sheet for Drinking Water Wells

Simple procedures for homeowners

The following well disinfection procedures may be carried out by homeowners on an existing well.  Disinfection is performed after the well is sampled and found to be total coliform or e-coli positive, or when the presence of non-pathogenic bacteria such as slime formers or iron bacteria have been identified.   A total coliform bacteria sample is used as an indicator of unsanitary conditions. If total coliform or e-coli positive samples persist after disinfection, then an experienced registered private water systems contractor should be contacted to professionally disinfect your well using superchlorination methods and the construction of the well should be evaluated.

Step 1. Pump the Well

Turn on as many faucets in the home as possible, and run the water for several hours (24 hours if possible) to waste in the yard or other drainageway.  The well should be heavily pumped to completely flush the well borehole and the geologic formation that supplies the water.  Do not discharge this water to the septic system, as it will cause the system to become overloaded.

Step 2. Determine the total volume of water stored in your well.

The volume of chlorine used for disinfection depends on the total volume of water stored in the well casing and the distribution lines (plumbing).  The total volume of water stored in the well casing can be calculated based on the total depth of the well and the static water level in the well.  Information on the total depth and static water level (water level under non-pumping conditions) of the well can be obtained from the well log.  The well log is a record of the construction, depth and geologic materials encountered in the well and is filled out by the water well driller.  After the well is drilled, copies of the well log are filed with the Ohio Department of Natural Resources, Division of Water, the local county health department, and a copy is provided to the well owner.  If you do not have a copy of your well log, search the ODNR website, or contact ODNR, Division of Water at (614) 265-6740.  The total depth of the well will be recorded at the right side of the well log, and the static water level will be recorded under the well test section of the well log.  Subtract the static water level from the total depth of the well to determine the total feet of water held in the well casing.

Step 3. Determine the volume of chlorine to use for disinfection.

Once the total feet of water stored in the casing is known, then the volume of water stored in the casing can be calculated based on Table 1.  Take the total feet of water stored in the well, and based on the well diameter, multiply the total feet times the appropriate gallons per foot of water.


Total well depth is 100 feet, static water level is 60 feet, well casing diameter is 5 inches.

100 feet - 60 feet = 40 feet of water in the well casing.

From Table 1, a 5 inch casing has 1 gallon stored per foot.

40 feet of water in the casing x 1 gallon per foot = 40 gallons volume of water in casing.

Table 1. Volume of water in well

Diameter of well (inches)

Gallons per foot of water











The total volume of chlorine to be used for disinfection can be calculated based on the Table 2.  For the example cited above (40 gallons of water in the well casing), use approximately one-half of the amount of chlorine necessary to disinfect 100 gallons.

Table 2. Amount of Chlorine added to 100 gallons of water for disinfection

Chlorine Concentration (parts per million)

Gallons of 5.25% sodium hypochlorite - liquid bleach

Pounds of dry calcium hypochlorite

Minimum contact time

250 ppm

0.5 gallon

0.38 lbs

8 hours

500 ppm

1.0 gallon

0.75 lbs

8 hours

If the total volume of water stored in the well casing is unknown then add two gallons of fresh 5.25 % unscented laundry bleach, also called sodium hypochlorite, to five gallons of water. Mix the solution in a new clean garbage can, or clean a garbage can and line it with a new plastic garbage bag.  Laundry bleach loses its? effectiveness the longer it sits on the shelf in the store or in your home. Solid chlorine pellets, which are 65% to 70% calcium hypochlorite, should be dissolved in a five gallon bucket of water. Be aware that some solid chlorine products used for swimming pools may have additional chemicals, such as algaecides, in them and should not be used for well disinfection.  Place the can next to the well to pour the solution or siphon the chlorine solution from the can to the well.

Step 4. Add the Chlorine solution.

Remove the cap from the well.  Pour the chlorine solution directly into the well.

Step 5. Add vinegar.

Add 1 quart of white vinegar to a five gallon bucket of water for each 100 gallons of water stored in the well.  If the total amount of water stored in the well is unknown, add 2 quarts of vinegar.  Add this solution to the well.

Step 6. Flush and recirculate.

With a garden hose, re-circulate this solution back into the well washing down the sides of the casing for approximately ten minutes. Debris may begin to slough off the side of the casing, and iron or manganese in the water may begin to turn solid as the chlorine reacts with the minerals.

Turn on all faucets connected from the well throughout the house and outside the house, including the hot water faucets.  Make sure to turn on faucets that rarely or never get used, especially yard hydrants and outside spigots.  Remember to run water into the washing machine and flush all toilets. Run the water until the chlorine smell is detected.  By-pass all water treatment units during the chlorination process to avoid damage to the resin bed.   The resin bed of the water softener can provide a place for bacteria to grow, and must be chlorinated at lower concentrations.   The water softener should be disinfected separately using ? to ? cup of chlorine bleach placed into the small fill tube in the large brine tank followed by a manual recharge. Remove and discard any carbon filters or cartridge filter elements and thoroughly clean the inside of the filter housing.

Step 7. Maintain sufficient contact time.

Once the odor of chorine is detected in all water lines, shut off the faucets and let the water sit in the plumbing for at least 24 hours.

Step 8. Flush the chlorine from the water system.

After 24 hours have elapsed, run the water to waste until the entire odor of chlorine is gone.  This will take a while depending on the volume of the well and the plumbing.   Do not run the water into your septic system as this will cause the system to become overloaded.

Step 9. Retest the well for total coliform.

Wait a few days, then contact the local health district to have another sample collected for total coliform bacteria. Make sure that the water is checked for chlorine before collecting the water sample. If there is any indication of chlorine in the water, the sample should not be collected. This helps avoid getting an indication of a safe sample that may be due only to the continuing activity of leftover chlorine and may not reflect the true condition of the water. Do not replace carbon filters or filter elements until a total coliform negative sample has been achieved.

What if the well tests positive for total coliform after disinfection?

There are many instances where the previously described disinfection procedures may not work in making a water well bacteria free. In some cases the pH of the water may need further adjustment in order to get the optimum disinfection from the added chlorine, or super-chlorination procedures may be required. The well casing may also need a thorough scrubbing or cleaning to remove non-pathogenic slime forming or iron bacteria that can build up on the well casing and borehole walls.  Removal of this type of bacteria often requires the use of specially formulated well cleaning products and drilling equipment and is best performed by a registered contractor. If total coliform or e-coli bacteria persist in water samples then contact an experienced registered private water systems contractor to professionally disinfect your well.  Contact your local health district when you experience any problems with your well or for assistance.

The Ohio Department of Health registers and bonds private water systems contractors.  Please contact your local health district or check the ODH list  (Download PDF Adobe Acrobat Reader Required - Download here if needed) of registered contractors.


The Fairfield Department of Health
1587 Granville Pike | Lancaster, Ohio 43130
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