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Disinfecting a Well

Any test which is marked unsatisfactory or unsuitable indicates an immediate need to evaluate and/or disinfect your water system.

Evaluation of the Water System

Prior to disinfection, the system should be evaluated to identify and correct possible sources of contamination.  Please Note:  Disinfecting the water system without first removing the source of contamination provides only temporary health protection.  The following list identifies some of the major health related factors to examine:

  • A sanitary seal that prevents surface water, insects, and rodents from entering the well
  • A ground surface graded or ditched so surface water drains away from the well or spring
  • Well casing surrounded by a concrete slab that extends at least 6 inches above the ground
  • Well or spring located at least 100 feet (for well) or 200 feet (for spring) from septic systems, barn yards, or other sources of contamination
  • Inverted, screened air vents on the well
  • No cross connection of the drinking water system with a non-potable system such as irrigation water.

Disinfecting Your Water

You can disinfect your well with household chlorine bleach such as Clorox or Purex or a generic brand.  The chlorine in the bleach kills bacteria.  Note that it may take more than one chlorination for your well to return a satisfactory test.  This is generally an overnight process so you will need to plan ahead when you decide to chlorinate.

The recommended minimum dosage is 1 gallon of bleach per 100 feet of well depth.  A high volume well will require more bleach than a lower volume well.  If you have previously disinfected your well, you may need to use more bleach the second time.  (Note: High level contamination requires more disinfectant.)

  1. Pour the bleach into the well.  You may need to remove the cap or a funnel may be necessary to get the bleach into your well.
  2. Run the chlorinated water through the distribution system.  This means go to every faucet (including outside faucets), turn it on until you smell chlorine and then turn it off.  If possible, run the chlorinated water back into the well and down the casing.
  3. Let the chlorine stand in the well and lines for at least four (4) hours.  Overnight is preferable.
  4. Flush the system using an outside faucet.  It is best to hook up a hose and run it down your driveway.  Chlorinated water should be disposed of away from streams, lakes, ditches, and lawn and garden areas.  Do not run the chlorinated water into your septic system, since this may kill bacteria which digest waste, and you may be overloading your system with water.
  5. When the well is flushed (no smell of chlorine), flush the remaining chlorine in the house lines by running water from each faucet inside and outside the house.
  6. Resample after a wait of 1 to 2 days.  This will help make sure no excess chlorine is in the water.

Professional Help

You may prefer to have a well or water supply professional chlorinate your system.  Look in the yellow pages under water purification, water treatment, well drilling, etc.

Temporary Measures

While waiting for chlorination to be completed, water used for drinking and cooking should be from a known safe supply.  You can perform emergency disinfection by boiling the water for 1 minutes, or put 4-10 drops of bleach into 1 gallon of clear water.  Stir and let stand 30 minutes.  At that time the water should have a slight chlorine taste, if not, add more bleach.  You can also use bottled water purchased from a store, or a known safe water supply.

Clallam County Health & Human Services
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