Hurricanes bring excessive rain. When heavy rains bring flooding to an area, your private well may not be safe to drink. It may be in danger of contamination from pollutants found in the flood waters. If your well has been flooded, meaning either your well head was surrounded by flood waters or it was submerged in flood waters, please read What Should I Do After My Drinking Well Is Flooded? for more details.

If your well water test reveals bacteria, the well and water system need to be disinfected. Non-scented chlorine bleach is often used to disinfect a bacterial contaminated well. Take the following steps to achieve an effective well disinfection.

Not all bleach is created equal!

It can be challenging to find disinfecting products right now. When you are looking for bleach to disinfect your well, please remember: DO NOT PURCHASE SPLASHLESS BLEACH.

Common household bleach usually contains 5-6% sodium hypochlorite (i.e. chlorine). Splashless bleach is a little thicker than regular household bleach. It is less likely to splash, but the sodium hypochlorite concentration is only 1-5%. It is not strong enough to sanitize and disinfect your well. As the label warns, you will be left with a lot of suds in your water! If you have already used the splashless bleach, you will need to flush your well system longer to remove all the suds.

Bleach expires too!

Bleach loses strength in its container over time. Check the “sell by date.” If you cannot buy new bleach, try to use bleach that is less than three months old. In addition, only use unscented bleach to avoid adding unneeded chemicals to the water.

Right pH is critical!

To make the disinfection procedure more effective, make sure the pH (i.e. acidity) of the water well is between 6 and 7.5. If the pH of your well is not in this range, consult a well treatment professional to adjust the pH and maintain it in the correct range during the disinfection process.

Prepare a chlorine solution!

Bleach should be combined with 10 parts of water before adding it to the well for the best results. It will reduce the chance of corrosion of the well system. Please note DO NOT mix chlorine solutions with other cleaning products, including ammonia, because toxic gases will be created. The amount of bleach depends on the depth of water in the well and the diameter of the well casing as shown in Table 1. For example, if your well diameter is 2″ and the well depth is 100 feet, you will need 1 cup of bleach with 10 cups of water before pouring it into your wells.

Table 1. The Amount of Chlorine Bleach to Use for Well Disinfection

*Table 1 is adapted from Florida Department of Health publication “What Should I Do If My Well Is Flooded?”

Well Water Disinfection Procedure

1. Pump out the well to remove any potential contaminants. It is at least three well volumes of water from a faucet near the wellhead, or at a minimum, pump the well for at least 1 hour before beginning the disinfection process.

2. Flush out household plumbing including the water heater. Make sure the water is clear and free of sediment.

3. Turn off electric power to the pump and remove the well cap. Prepare a solution of bleach and water, and pour the solution into the top of the well. The amount of bleach depends on the depth of water in the well and the diameter of the well casing (Table 1). The bleach should be diluted with 10 parts of water. For example, 1 cup of bleach with 10 cups of water before pouring it into your wells.

4. Recirculate the water by connecting a hose to a faucet and spraying the water back into the well for at least 10 minutes.

5. Open every faucet in the system and let the water run until the smell of chlorine can be detected. Then close all the faucets and seal the top of the well.

6. Allow the chlorinated water to stand in the system for at least 12 hours but no longer than 24 hours. You cannot use any water through the system during this period including flushing your toilets. Prepare an alternative water supply during the well disinfection process.

7. The next day, operate the pump by turning on all faucets, beginning with outside and flushing out the water until there is no chlorine odor.

It is not a regular maintenance!

This well disinfection method is also called Shock Chlorination. Please note shock chlorination is not a regular maintenance method. This disinfection method is only used when a new well is drilled, flooding occurs, if bacteria is found, or if the well has been sitting without use for an extended period of time. After you shock chlorinate the well, you need to retest the water well to make sure it is free of bacteria.

Please note to retest the well water in 5 to 10 days. If bacteria is still present, you may need to repeat the process to remove long-established bacteria colonies. If the problem persists, you need to contact a water treatment professional familiar with bacterial contamination in wells.

Additional Resources

Private Wells 101: Bacterial Contamination and Shock Chlorination https://edis.ifas.ufl.edu/publication/SS700

Household Drinking Water Testing for Public and Private Water Supplies https://edis.ifas.ufl.edu/publication/SS712

Private Well 101: Drinking Water Standards https://edis.ifas.ufl.edu/publication/SS297

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