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Department of Health and Senior Services provides Water Safety Information Related to Private Water Supply Wells

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Department of Health and Senior Services provides Water Safety Information Related to Private Water Supply Wells

The Missouri Department of Health and Senior Services issued guidance today on the safety of wells and private water sources that have been subjected to flooding. If the well casing is submerged in floodwater, DO NOT USE THE WATER. Water from submerged wells cannot be safely sanitized. When floodwaters recede, small quantities may be disinfected until the well can be properly chlorinated.

After floodwaters recede, wells can be disinfected with chlorine. A convenient form to use is sold commercially in grocery or other stores as liquid chlorine laundry bleach. Most of these products contain 5.25 percent solution or more of sodium hypochlorite when fresh, and is equivalent to 5 percent available chlorine.

As water is used pressure drops, and at a preset limit the pump turns on creating a short surge. A pump not running for a period of time due to a power loss is no different than the family leaving the home for a period of time and not using water. Unless there is some risk factor compounded by the power outage there is minimal risk of contamination during the outage.

Other factors of concern that could compound with an outage to negatively influence water safety may include:

Known system problems, such as line breaks or system leaks;
Past system problems, including a history of unsafe samples;
Hoses left in stock watering tanks, swimming pools, or other unsafe water sources without a backflow prevention device at the time of the outage;
The loss of power disables a water disinfection system, such as a UV light or chlorination system. Private well users uncertain as to the functioning of their disinfection system after the outage, or the quality of water stored during the outage, should contact a water service professional (system installer) or local health department; and
The pump is damaged due to the power surge and must be pulled and replaced.

Under these circumstances, testing the well for bacterial condition and disinfecting the system may be advisable. Information on well disinfection from the Department of Health and Senior Services is located at

NOTE OF CAUTION: Fragrance-free chlorine, whether used as sodium hypochlorite or calcium hypochlorite is a strong oxidizer and should only be used strictly following label directions. Avoid skin or eye contact and after chlorination flush the system completely, preferably through an outside tap into a non-grassy area before consuming, bathing, using for laundry, or use in an aquatic environment (fish tanks).

All homeowners using private wells are encouraged to test the water at least once a year, regardless of any power interruption. For homeowners who do not know the past history of their well or who have lingering concerns about their water quality they may choose to have their well tested at this time.

Water testing kits and additional detailed information on well disinfection can be obtained by calling your local public health department or the Missouri Department of Health and Senior Services at 573-751-6080.

NOTE: Residents who are on public water systems should follow the instructions of their local water utilities.