Disinfection of Bored or Dug Wells After an Emergency

Bored and dug wells can be difficult to disinfect because the shallow depth and inadequate protection from flood water can allow contaminants to re-enter the well.
Follow these steps to disinfect bored or dug wells:

1. If the well has an electrical pump, turn off all electricity and clear debris from around the top of the well.
2. Repair the electrical system and pump if needed. Contact a qualified electrician, well contractor, or pump contractor if you are not experienced with this type of work.
3. Start the pump and run water until it is clear. Use the outside faucet closest to the well to drain potentially contaminated water from the well and keep unsafe well water out of the interior household plumbing. If there isn’t a pump, bail water from the well with a bucket until water is clear.
4. If the well is connected to interior home plumbing, close valves to any water softener unit.
5. Use Table 1 below to determine the amount of liquid household bleach needed to disinfect the well. Use only unscented bleach. For a table in metric units, please see Table 1.1: Approximate Amount of Bleach for Disinfection of a Bored or Dug Well (Metric) below.
6. Using a 5-gallon bucket, mix the bleach from Table 1 with 3-5 gallons of water (12-19 liters).
7. Add the bleach water mixture to the well. Avoid all electrical connections. Attach a clean hose to an outside faucet and use it to circulate water back into the well for thorough mixing. If there isn’t a pump, mix water by pouring it back into the well using a bucket.
8. Rinse the inside of the well casing with a garden hose or bucket for 5-10 minutes.
9. Open all faucets inside the home and run the water until you notice a strong odor of chlorine (bleach) at each faucet. Turn off all faucets and allow the solution to remain in the well and plumbing for at least 12 hours.
10. After at least 12 hours, attach a hose to an outside faucet and drain the chlorinated water onto an area without plants or other vegetation, such as a driveway. Continue draining until the chlorine odor disappears. Avoid draining into open sources of water (streams, ponds, etc.).
11. Turn on all indoor faucets and run water until the chlorine odor disappears.
12. Until well water has been tested, boil it (roiling boil for 1 minute) before using or use another alternative water source. Wait at least 7-10 days after disinfection, then have the water in your well tested. Water testing cannot be done until all traces of chlorine have been flushed from the system.

• Wait at least 7 to 10 days to test the water after disinfection to ensure that the chlorine has been thoroughly flushed from the system. Until well water has been tested, boil it (rolling boil for 1 minute) before using or use another alternative water source.
• Contact the local health department for water sampling and testing information or contact your state laboratory certification officer to find a certified lab near you. You can also get water sampling information from the U.S. Environmental Protection Agency’s Safe Drinking Water Hotline (800-426-4791).
• Sample the water for total coliform and either E. coli or fecal coliform bacteria to confirm that the water is safe to drink.
• If the results show no presence of total coliforms or fecal coliforms, the water can be considered safe to drink.
• Follow up with more water tests, one in the next 2 to 4 weeks and another in 3 to 4 months.
• Check the safety of your water over the long term, continue to monitor bacterial quality at least twice per year or more often if you suspect any changes in your water quality.

If results show the presence of any coliform bacteria, repeat the well disinfection process and test again. If tests continue to show the presence of bacteria, contact your local health department for assistance.

Bored and dug wells can be difficult to disinfect because of how they are constructed. Many are shallow and have no lining, casing, or grouting, which can allow contaminants to enter the well from the land surface or upper soil levels. If contamination problems continue, consider upgrading the existing well or drilling a new well.

The disinfection process may damage water softeners due to the large amounts of chlorine used. Follow your manufacturers’ instructions for appropriate methods to disinfect your softener unit. You will need to bypass the unit until the disinfection process is complete.