Chlorinating Private Water Supplies

Well chlorination is a disinfection process that uses chlorine in a well to kill potentially harmful microorganisms. Any newly installed well, repaired well, or well that the well cap/seal has been removed for any reason should be considered contaminated unless a well disinfection/chlorination has been performed.

The bacteria that contaminate the water are common in the soil and on most surfaces, and can enter the well during the construction phase of well installation or during any type of repair work. Therefore, complete and proper disinfection of the well and water system is a necessity after the construction, repair, and maintenance of any well.

When a sample of water is sent to the lab and the analysis indicates the presence of coliform bacteria, proper disinfection is a logical first step to take to eliminate the contamination in a well. Proper chlorination is also needed when the analysis indicates the presence of nuisance bacteria. Some wells may actually need a more continuous form of chlorination to provide a safe source of drinking water.

The Story County Environmental Health Department always recommends that you hire a professional to disinfect your well. Working with chlorine in high concentrations can be hazardous and if you hire a registered well driller or another service professional who is knowledgeable of private well components, including filtration equipment, they will understand the proper safety procedures to ensure a proper job is completed. Additional information may be needed including, complete well information, i.e. depth, well diameter, and static water level so that the exact chlorine requirements for proper chlorine concentrations can be established.

If you choose to perform chlorination of your private water supply well yourself, always use proper safety precautions when working with all types of chlorine. Common precautions may include proper ventilation, eye protection, respiratory mask, long sleeves, heavy work clothing and gloves. In addition to the hazard that the chlorine poses, you must remember that most wells have a pumping system that include live electrical wiring enclosed within the well casing and this can pose a shock threat if faulty wiring exist or you improperly handle wiring. There may be other precautions that are required which will vary with the type of well on your property. Please contact a water professional or contact us at the Story County Environmental Health Department for more details.

A typical chlorination procedure is described below. If your well has water treatment equipment device(s), it is recommended that you contact the manufacturer of the unit or your well driller for information regarding any effect chlorination may have on the system.

1. Disconnect the pump power source (turn off breaker or fuse box). Remove the vent or well cap from the well and insert a clean funnel into the opening.

2. Add the correct amount of chlorine to a clean bucket that has been partially filled with water (amount of chlorine is determined by diameter of well, amount of standing water, and capacity of storage system) Add the chlorine to the water NOT the water to the chlorine.

3. Pour the chlorine solution into the well through the funnel and let it settle into the well for 2-3 hours. Use caution around and avoid handling any wiring in the well casing during this step as a shock hazard may exist.

4. Attach a hose that will reach the well to a faucet near the well head. Turn on the water and recirculate through the hose and into the well for 10-20 minutes being sure to thoroughly wash the inside walls of the casing. Use caution around and avoid handling any wiring in the well casing during this step as a shock hazard may exist.

5. Turn off the water and remove the hose from the well . Reinstall the vent or cap. Use caution around and avoid handling any wiring in the well casing during this step as a shock hazard may exist.

6. Go to the outside faucet that is the furthermost from the well. Open the faucet and run the water until the chlorine odor can be detected. Turn off the faucet. Go to the other outside faucets and run the water until a chlorine odor is detected, then turn off the water.

7. Proceed to all inside plumbing fixtures. Run the water until chlorine odor is detected, and then turn off the faucet.

8. Allow the chlorinated water to stand in the well and the water system for a minimum of 12 hours. Care should be taken to ensure that animals and people have non chlorinated water to drink during this time as the high concentrations of chlorine in the well water will make it unusable for consumption of any kind.

9. After 12 hours, the treated water may be run off through an outside faucet until the chlorine odor can no longer be noticed. If your well will not produce water continually, monitor your running water or you may experience serious pump damage. After the chlorine is no longer present outside, the inside faucets may be run off.

NOTE: Heavily chlorinated water must not be discharged into the septic system or over the drainfield area because the waste system may stop functioning properly.

10. A chlorine test kit is recommended and can be used to determine that all of the chlorine has been discharged from the well and plumbing fixtures.

11. A water test can be taken at any point 10 or more days after the last chlorine odor is noticed and submitted to a certified water testing lab for analysis. 

It should be noted that some types of wells like flowing artesian wells or wells deriving their water from fractured limestone may need special procedures to accomplish a thorough chlorination as these features may prevent proper dispersal of chlorine throughout the well and subsequent disinfection treatment. Please contact us for more information or to arrange water testing.

For basic information on chlorinating water supply wells, please read the attached documents below.

Good Wells for Safe Water (PDF) - A publication of Iowa State University Extension Service.

Coping with Contaminated Wells (PDF) - A publication of Iowa State University Extension Service.

If you need additional assistance on evaluating your well problem or more information about well chlorination or water testing for your private water supply well, please contact us.