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
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
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
Chlorine Concentration (parts per million)
Gallons of 5.25% sodium hypochlorite - liquid bleach
Pounds of dry calcium hypochlorite
Minimum contact time
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
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
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
What if the well tests positive for total coliform after
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
Please contact your local health district or check the
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of registered contractors.