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Protect Your Health by Chlorinating Your Well

by Ron Kurtus (updated 19 February 2012)

If you have a private well that supplies drinking water to your household, you may occasionally have to have that well chlorinated to protect against bacteria that may have contaminated your water.

The chlorination process is relatively simple, although many people hire professionals to do the job.

Questions you may have include:

This lesson will answer those questions. Health Disclaimer

Well contamination

The water in my household comes from our 300 foot deep private well. In 1998 a severe rainstorm flooded our community, and we found that our well water was contaminated with bacteria. It may or may not have been caused by the flood, but it is something that must be taken care of immediately.

After some research, I found information on how to remove the bacteria from a private well. This essay explains how to chlorinate your well.

How bacteria gets in well

There are several ways that bacteria can get into a well. Often, after a flood many wells in the area become contaminated with bacteria. This can happen if the wellhead gets submerged, allowing dirty water to leak down into the well.

It can also happen by excess water draining into the well aquifer—or underground source of water—without being properly filtered through the ground. Shallow wells are more likely to become contaminated than deep wells.

Types of bacteria

The types of bacteria that usually contaminate wells are coliform and E. coli bacteria. These often come from animal waste. This type of bacteria can cause stomach discomfort and diarrhea. E. coli bacteria can cause serious illness and even death.

Check your well

Private wells should be checked periodically and especially after flood conditions.

Method to check the water

The method to check the water is to let it run until you are getting fresh water from the well. It is preferred not to test water that has been sitting in your pipes. Then you collect the water in a sterile container and bring it to a testing agency. Local government agencies or private well inspection companies will check the water for contaminants.

Check for other contaminants

Besides having the water checked for bacteria, it is also wise to have it checked for metal contaminants, petroleum products and pesticides. Each requires a separate check.

Chlorinating your well

To disinfect your well and eliminate the bacteria, you should chlorinate the well. You can hire a company that services wells to do the chlorinating. The cost ranges from $80 - $200.

You can also perform the task yourself. It simply consists of pouring diluted chlorine into the water, letting it sit for a while, and then flushing the chlorine out of the system. You do this by making preparations, adding the chlorine bleach, and disinfecting the well. The following explains how to do this.

Make preparations

Before you start, you should make some preparations.

  1. Determine where you wellhead is and how to remove the top.
  2. Determine the quantity of bleach to use. (The quantity depends on the size and depth of your well. See chart below.)
  3. Buy the necessary quantity of unscented chlorine bleach from the store.
  4. You want to to mix the disinfectant evenly throughout the water in the well and to force it into surrounding water-bearing rocks. It also prevents the concentrated chlorine from corroding the metal pump or other metal parts in the well.
  5. Get containers ready to dilute the chlorine with water. There are several opinions (taken from the references at the end of this lesson) on what mixture to use:
    • One method says to mix in a ratio of 1 part chlorine bleach to 100 parts water in a new garbage can. Figure on using enough to meet or exceed the total volume of your well. Plan to put the solution in your well 25 gallons at a time.
    •  Another method says to mix 1.5 quarts of bleach with 6 to 10 gallons (3 or 4 buckets) of water for a 6 inch diameter x 100-foot well (4.5 quarts with 30 gallons for a 6 inch x 300-foot well).
    • A third suggested mixture is 3 quarts of bleach and 36 quarts or 18 gallons of water (a 1 to 12 ratio of bleach to water) for a 6x300 well. This could be done by mixing about 1 1/2 cups of bleach in a gallon container of water. This is the method we used.
  6. Turn off your water heater.
  7. Turn off your water softener, so it won’t recycle during the chlorinating process.
  8. Identify all your water faucets, according to distance from the well.
  9. Remove aerator screens from all the faucets.

Amount of chlorine bleach to use for disinfecting wells

Chlorine required


100 feet

200 feet

300 feet

400 or more







4 inches


1/2 qt.

1 qt.

1 1/2 qt.

2 qt.

6 inches


1 qt.

2 qt.

3 qt.

4 qt.

8 inches


2 qt.

4 qt.

6 qt.

8 qt.

Add chlorine bleach

Now you can go through the process of killing the bacteria in your well.

  1. Check the area around the top of the well for spiders and especially earwigs. You don’t want any to fall into your well when you remove the cover.
  2. Remove the top of the well.
  3. Pour the chlorine-water mixture into the well.
    • One method is to pour the diluted solution directly into the pipe, trying to coat the sides of the well casing as you pour. If you get chlorine on the pump or wiring, flush thoroughly with fresh water so the metal doesn't corrode.
    • Another method is to use a hose and put it as far down as you can into the well and to pour the chlorine with a funnel through the hose.
  4. Rinse down the sides of the well casing with a garden hose that is connected to the system being chlorinated. This will circulate the solution throughout the water system. Run the water until you can smell chlorine from the hose. It should take 5 - 10 minutes.
  5. Cover the well and make sure it is sealed.

Kill the bacteria

Next, you want to get the chlorinated water throughout your water system in your house, so that it will kill all bacteria.

  1. Starting with the faucet closest to the well, open your faucets and run until you can smell the chlorine or bleach smell.
  2. Then allow things to sit for from at a very minimum of 4 to 24 hours or longer.
  3. Then thoroughly flush out your water system until you no longer smell the bleach. This may require running the water for up to 2 hours.
  4. After several days, have your water checked for bacteria again.
  5. Then check it once more after a few months.

If the water becomes contaminated again after a short time, you had better try to find the source of contamination.

(Note: After chlorinating your well, rust often gets into the water and can even temporarily clog your pump filter. Usually the rust settles and things get back to normal after a short while.)


Although you can hire professionals to chlorinate your well, it is possible to do the job yourself. After contamination, the wells should be checked again to make sure that the contamination wasn't just a random occurrence.

Good water is most important for good health

Resources and references

Ron Kurtus' Credentials


How to Chlorinate Your Well Water - New Brunswick, Canada

How to Shock Chlorinate or Disinfect Your Private Water Supply or Water Well - Water Research Center

Treatment Systems for Household Water Supplies - North Dakota State University - Water Quality

General Health Resources


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