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Whatcom County Health Department
Drinking Water Program, Environmental Health Division
Phone: (360) 676-6724
E-mail: Environmental Health


Drinking Water Program

Private Well Disinfection Directions

If your water sample showed bacteriological contamination, (unsatisfactory for coliform bacteria, fecal coliform or E.coli), you can follow the directions below for disinfecting the well and pipes. The water should be resampled about one week after bleaching (i.e. chlorinating) the well.

Note: Do not drink the water if coliform bacteria were found by the laboratory. The coliform bacteria indicate there may be a potential risk of illness if you consume the water. Boil the water for 10 minutes before drinking or using in food preparation to avoid the risk of illness.

Disinfection Procedures:

  1. Use one gallon of regular (no perfumes: i.e. “lemon scent,” etc.) household bleach that contains sodium hypochlorite. WARNING: There are new household bleaches on the market that do not contain any sodium hypochlorite. Read labels carefully and look for bleach that contains sodium hypochlorite as an ingredient. Please call our office if you have any questions.
  2. Mix the bleach in 5 to 10 gallons of clear water. Pour half of it directly into the well. If possible, pour the remainder in so that the sides of the casing are washed down. To fully distribute the bleached water in the well, run a garden hose down the well and let it run for 5-10 minutes. This will circulate the bleached water from the well, through the hose and back to the well again.
  3. After the bleach is added, turn on some taps in the house until the odor or taste of bleach can be detected, then turn them off. Do the same for all other taps and faucets. If you have a treatment system for your water, you may need to by-pass the treatment unit so it is not damaged by the bleach. If you share the well with someone else, let them know you are disinfecting the well so they do not inadvertently do a load of laundry or take a shower with the bleach water.
  4. Allow the bleach water to remain in the well and pipes overnight or for 24 hours if possible. Turn on the outside taps (to avoid over
    loading the septic system) until the smell of bleach can no longer be detected. Then do the same with the taps inside the house.
  5. After about 1 week of use, or after bleach is not detected with a test kit, submit another sample to the laboratory for analysis.

Well Construction Features:

A well constructed as follows will help improve water quality:

  1. A tight cover with a screened vent is needed to keep contaminated surface water, debris, and insects from entering the well.
  2. The well casing should rise at least 6 inches above the ground surface to protect it from flooding or ponding of water.
  3. A water-tight casing with solid joints should be sealed on the outside with bentonite clay or cement to a minimum of 18 feet below the ground. Finding a copy of the driller's well report will help confirm the proper construction of your well. Our office has some driller's well reports on file, otherwise contact the driller or previous owners.
  4. The well should be located at least 100 feet from any source of contamination such as a septic drainfield, privy, manure storage and spreading, or stream and lake.


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