The contractor is responsible for properly disinfecting any new well or well subjected to repairs or pump maintenance, upon completion of the work. Likewise, a pump installer must disinfect the well after the pump is installed, or repaired. Sufficient chlorine solution should be introduced into the well and water system to insure a minimum dosage of 100 milligrams per liter (mg/l). This chlorine solution should remain in the well and water system for a minimum of 24 hours. However, after 24 hours at least 25 mg/l of chlorine should still remain in the water. Under these conditions the well need not be disinfected again until the pump is set.


When working with chlorine, a person should be in a well-ventilated place. Chlorine powder or liquid should not come in contact with the skin or clothing. Chlorine solutions are best handled in wood, plastic or crockery containers because metal containers will corrode.


Every new, modified or reconditioned water source, including pumping equipment and the gravel used in gravel wall wells, should be similarly disinfected before the well is again placed into service. Such treatment should be performed when the well work is finished and again when the pump is installed or reinstalled.

  • Use Table 6 to determine the amount of water in a drilled or driven well, based on casing size and the total depth of the well:

Table 6: Water in Gallonage of a Drilled or Driven Well

Diameter of Well Casing in inches Gallons per foot
5 1.00
6 1.50
8 2.60
10 4.10
  • For each 100 gallons of water in the well, calculated from Table 5 above, use 3 cups of liquid laundry bleach (5.25% chlorine) or 2 ounces of hypochlorite granules (70% chlorine). Mix the calculated amount of chlorine in about 10 gallons of water. For your convenience in measuring out the correct amount, the following conversion factors are listed:
    • 2 cups equals 1 pint
    • 4 cups equals 1 quart
    • 16 ounces equals 1 pound
  • Pour this solution into the well making sure the casing walls are wetted before the seal or cap is installed.
  • Connect one or more hoses to faucets on the discharge side of the pressure tank and run them into the top of the well casing. Start the pump, circulating the water back into the well for a least 15 minutes. Then open each faucet in the system until a chlorine smell or taste appears. Close all faucets. Seal the top of the well.
  • Let stand for at least 12 hours, preferably 24 hours.
  • After standing, run the pump to discharge water from each outlet until the chlorine odor and taste disappears.