Chlorination

For well water bacterial treatments

Chlorination is used in water wells to kill bacteria. New wells are disinfected at the time of drilling. Older wells have a risk of contamination by microorganisms and all wells should be tested at least two or three times a year. The probability of contamination is greatest in a number of conditions. These include:

  • in early spring
  • after a prolonged dry spell
  • after a significantly heavy rain
  • after extended periods of non-use

You can have your water tested by state officials (depending on your state of residence) or by independent labs.

If you have experienced any gastrointestinal illness and you fear that it may be related to your well water you should see a physician before anything else.

Total coliforms
Total coliforms do occur naturally in soil, only because of the presence of animal (or even human) waste, though. Total coliforms should never exceed 10 per 100 mL of water. Of course, if there are any coliforms this renders the water any marginally safe to drink. If there is the presence of E. coli, serious steps should be taken to decontaminate the water.

This is the most notorious coliform, its full name Escherichia coli. Its presence indicates certain fecal contamination. This can cause serious long term health effects or death.

Chlorine disinfection
You can perform your own chlorine disinfection, according to the table below.

All figures assume that you have a drilled well with a standard casing diameter of six inches. Older wells have a larger diameter. If your older well has a diameter of one yard, it will require up to 30 times as much chlorine for the same well depth.

Depth of water in well

New well

Existing well

1.0 yards

3 oz.

1 oz.

3.0 yards

10 oz.

2 oz.

5.0 m

1 pint

3 oz.

10.0 m

1 quart

200 mL

* New wells require a higher concentration of chlorine: 250 parts per million (ppm). Existing wells require approximately 50 ppm chlorine.
Administering chlorination:

  1. Add the amount of unscented bleach as determined by the table above. Wash down the inside of the well with a garden hose to ensure thorough mixing in.
  2. Start the well pump and bleed all air from the pressure tank. Open every tap in the house and other buildings. Allow water to run through until you detect the smell of chorine.
  3. Shut off taps and allow the water to sit in your system for up to 24 hours. No baths, no cooking and no water usage of any kind should be allowed. You might want to put notes on the taps to remind yourself, children, etc.
  4. Start the pump after 24 hours and run water out of your system and away from buildings where the chlorine (a very harmful chemical in itself) will do no harm.
  5. Wait another 48 hours then sample the water and retest it. If you absolutely need to use your water you can boil it for several minutes before using it.
  6. If the shocking works, you should repeat the test two to four months.
  7. If the shocking does not work after two attempts, you almost certainly have a source of continuous contamination. You will need to take proper steps with the authorities and you may need to drill a new well.
Guide 2 Water Filters