Environmental lands DepartmentHow Do I disinfect my well?

If Your Water Isn’t Safe

If a water test indicates your water supply isn’t safe, you may be able to find a new source of water or install water treatment. In the meantime, you can bring water from a safe water supply. If you choose water treatment, be sure it is adequate to remove those contaminants that are causing a health risk.

The Purpose of Disinfection

If bacteria or other living microorganisms have contaminated your private water supply or well, proper disinfection should kill them. It can make water safe until a sanitary supply is secured. Disinfect the well whenever it has been flooded or open for maintenance or repair. By disinfecting you may also be able to reduce nuisance bacteria that cause odor or aesthetic problems.

Ways to Disinfect

Water can be disinfected with heat, chemicals or light, depending on your situation.

  • Boiling. This will kill bacteria and parasites such as cryptosporidium. First make sure nitrate is not in your water, because boiling will concentrate whatever nitrate is. Where ever The Center for Disease Control and the Minnesota Department of Health recommend bringing water to a rolling boil and boiling it for one minute.
  • Chlorine. This is the chemical most often use to shock-chlorinate private wells. You may hire a professional or, if you want to do it yourself, go to www.extension.umn.edu/distribution/naturalresources/DD5941.html for more detailed instruction on how to shock-chlorinate your well safely and effectively.

Shock-chlorination is appropriate when the well has been contaminated through a one-time event such as a flood or during maintenance. It is not a long-term solution for an unsafe well with continuous contamination, such as one with a damaged well casing. Shock-chlorination may also be effective in reducing nuisance bacteria that do not present a health risk.

The two most important considerations are chlorine concentrations and exposure time. You’ll need enough chlorine to kill the living organisms, but don’t want so much that it damages your pump, plumbing, or septic system. Too much chlorine can take a long time and a lot of water to flush from the system. The entire plumbing
system must be exposed to the chlorine for an adequate amount of time to ensure complete disinfection. The chlorine should remain in your household plumbing system for 6-8 hours.

  • Ultraviolet light.
  • Some countertop water treatment models use ultraviolet light to disinfect water. However, the systems have limitations: the water must be filtered and free of iron and other compounds, that could interfere with the ultraviolet light’s ability to penetrate cell walls to kill living organisms.

A Note of Caution

Disinfection isn’t a substitute for a permanent, safe water supply. It can help make water safe until a sanitary supply is secured. If your well is contaminated, boil water, carry water from a safe source, or buy bottled water. Disinfection is only effective against living organisms and will not improve water contamination by nitrate, arsenic, or other chemicals.

Contact Us

(218) 335-7400 DRM

Name Title Phone
Brown, Levi Environmental Director 335-7417
Harper, Jeff Water Resources Program Manager 335-7415

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