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Private drinking water supplies

How to disinfect private wells

Private wells may occasionally be flooded or otherwise contaminated and are apt to cause sickness unless properly treated. Flooding and cross contamination may carry waste materials from barnyards, sewers, septic tanks, cesspools and pit privies into the well. Water from wells flooded or contaminated should not be used for drinking purposes unless it is boiled or otherwise disinfected and the well properly treated to remove contamination. New wells should also be disinfected before use.

To reclaim a contaminated well, it should first be pumped heavily to remove as much of the contaminated water as possible and then treated with a strong chlorine solution. Chlorine for this purpose can be obtained from any grocery store in the form of laundry bleach sold under such trade names as HILEX, CLOROX, PUREX, etc.

If possible, determine the amount of water in the well and add the amount of chlorine compound necessary to give a dosage of 50 mg/1 into the opening between the casing and the drop pipe. On well repair, the chlorine should be added just before installation of the pumping equipment.

Disinfectant required for a dosage of 50 mg/1 chlorine:

Disinfectant required for a dosage of 50 mg/1 chlorine
Diameter of Well, Spring or Pipe in Inches Gallons of Water per Foot of Water Depth Ounces of Disinfectant per 10 ft Dept of Water
5.5% Sodium Hypochlorite*
2 0.16 0.20
3 0.37 0.46
4 0.65 0.80
5 1.00 1.25
6 1.47 1.87
8 2.61 3.33
10 4.08 5.20
12 5.88 7.46

*Sodium Hypochlorite, known as laundry bleach, can be purchased at most grocery stores.

If water volume cannot be determined, use 1 quart of laundry bleach mixed with 3 gallons of water.

Chlorine can destroy only the bacteria with which it comes in contact. Agitation of the water in the well may be required to assure thorough mixing. After adding the chlorine, start the pump and operate until the odor of the chlorine is detected at the pump discharge. To disinfect the storage and distribution system, open the house faucets and let the water run until the odor of chlorine is apparent. Allow the chlorine solution to remain in the well and distribution system for a period of 12 to 24 hours before using. Pump the well and flush the distribution system to remove all traces of chlorine.

After pumping and flushing all chlorine from the system, a water sample should be collected and submitted to the Fargo Cass Public Health laboratory for a bacteriological analysis to assure the safety of the water supply. Sample containers are available on request. If contamination is still shown to be present in the water supply, the chlorination procedure should be repeated.

For further information, contact Fargo Cass Public Health at (701) 241-1360.