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Guide to Shock Chlorination for Private Wells

Shock Chlorination: How to Get Rid of Bacteria in Your Well Water


So, you just found out that bacteria live in your well water… 

Never fear. This guide give you a clear method for treating your drinking water to remove coliform, E. coli, and other potentially harmful bacteria living in your well water and pipes.

The method we suggest and describe below is broadly called “Shock Chlorination.” It's an affordable, do-it-yourself way to disinfect your well and water lines.

When To Use Shock Chlorination:

If the bacteria live in your well and your pipes then there is hope for shock chlorination to work. If the source of your bacterial problem is your groundwater or your city water system, however, then chlorinating your system will not have the desired effect and bacteria will quickly repopulate your well and distribution system.

If the bacteria not just in your well and pipes, your source water may be contaminated or you may have a running leak from a nearby septic system tank. In these cases, you will need to employ a different method for routinely controlling bacteria in your water. Rather than a “shock” treatment, you will require water treatment like UV, RO or a chlorine drip filter. Learn about water treatments.

If you’ve tested your water and detected certain types of bacterial or viral contamination, then shock chlorination is probably a viable solution for you and your home.

Disinfection by chlorine

Chlorine kills bacteria and other microbes through a process of oxidation. There are certain microbes for which this works very well, but then there are other microbes which are resistant to such disinfection by chlorine.

Microbes readily killed by chlorine:

  • Gram-negative bacteria
  • E. coli
  • Coliform bacteria
  • Most iron bacteria
  • Most sulfur bacteria
  • Salmonella
  • Certain virus strains like Hepatitis A
  • Some forms of Giardia
  • Legionella
  • Campylobacter
  • Staphylococcus
  • Poliovirus
  • Rotavirus
  • Adenovirus
  • Cholera
  • Klebsiella
  • Shigella
  • Microbes not killed by chlorine:

  • Cryptosporidium
  • Some forms of Giardia
  • Chlorine Water Disinfection

    Will shock chlorination work for my well?

    Although the general operation and function of most drinking water wells is quite similar overall, it is important to understand that different wells will employ different systems and components. While we do provide a solution for the most common types of drinking water wells, it is possible that your well has idiosyncrasies which our instructions may overlook.


    Talk to an expert

    Shock Chlorination Advisory: Don’t drink the water!

    The shock chlorination method is a common procedure for disinfecting drinking water by adding a very high amount of chlorine to a water system. Here are some very important things to read through and understand before performing shock chlorination on your water.

    Do NOT drink (or use) the water during disinfection

    During the disinfection process, NO water from the system is safe to drink or consume in any manner. No human beings or animals should be in contact with the water during a period of at least 12 hours after beginning the shock chlorination process. If possible, no toilets or faucets should be used at all during this time.

    Are you ready? Pre-shock chlorination checklist

    💧 Plan to Use Other Sources of Water

    Plan ahead. You should have an alternate source of water available for up to 24 hours after you plan to perform shock chlorination on your well.

    💧 Turn Off Sprinklers and Other Automated Water Features

    Shock chlorination is most effective when your chlorine mixture reaches all ends of your water system. You want your chlorine to come in contact with as many potentially contaminated surfaces as possible–nozzles, spigots, tanks, hoses and fixtures alike.

    But you want to bypass equipment that is sensitive to chlorine (see carbon filters below) and you want to be sure that all of these appurtenances, especially sprinklers and other automated water features are set to the OFF position during your Chlorine Shock. You don’t want highly chlorinated water spraying all over your lawn!

    💧 Disconnect or Bypass Any Carbon Filters

    If you have carbon filters for water treatment installed in your home, you’ll want to remove or bypass them during the period of shock chlorination. The high level of chlorine used in shock chlorination can permanently damage carbon filters.

    💧 Don’t Touch

    Do not allow chlorine bleach to come into direct skin contact. We suggest wearing rubber gloves, goggles, and a chemical-resistant apron when handling your disinfection materials. These can be purchased at your local hardware store (or on Amazon).

    If accidentally you do come into contact with chlorine, flush the affected area with clean water (i.e. your alternate water source for the post-chlorination phase) immediately.

    💧 Plan Ahead for Safe Disposal of Chlorinated Flush Water

    After shock chlorination is complete, be sure not to dispose of the chlorinated flush water directly onto any livestock or plants. You’ll want to flush this used chlorine water in a safe way like a nearby ditch or drain.

    Do NOT dispose of this water into a small stream or pond as it will cause harm to aquatic life. Please plan ahead to determine where you will dispose chlorinated flush water.

    💧 Purchase Supplies

      • Water test: To confirm you have a coliform or e.coli or other bacterial problem. This Total Microbiology Water Test will be just the test to help. This all-inclusive pathogen and microbiological screening provides identification and enumeration of thousands of species of bacteria, protozoa, algae and more in well water.

      • Liquid household bleach: Must have 5.25% chlorine for disinfection to work properly. Do not use bleach with anything else added like fragrance or scent. As a rule of thumb, 1 gallon of bleach can disinfect an 8-inch diameter well holding approximately 100 feet of water.

      • Large bucket, 10 gallon volume: You’ll use this to mix your bleach with water so that you have more disinfectant solution to work with and promote better mixing.

      • Garden hose (or equivalent):This you’ll use to wash down your well and circulate your disinfectant. 

      Well Water Chlorine Shock Disinfection Instructions

      Step 1 - Locate Your Well

      Locate your well, remove the sanitary seal, or access plug.

      Step 2 - Calculate the amount of chlorine

      Use the table below to determine how much chlorine bleach you will need for disinfection. If you have a recent Water Well Bore Report then you can look at it to see how deep your well is and how high the water level is. Otherwise, you can use this table to estimate the amount of chlorine bleach you will need:

      Well disinfection

      Step 3 - Preparing your chlorine bleach

      With the right amount of chlorine bleach for your well measured out, mix it with some regular water so that you have more volume of disinfecting solution to work with. Having more volume will help to ensure your disinfectant is properly mixed throughout the well surfaces.

      To this end, we advise that you prepare 4 and 8 gallons of chlorine bleach and water mixture in your 10 gallon bucket.

      Well disinfection

      Step 4 - Pour your mixture into the well

      Pour the disinfection chlorine contents down your well casing. If the 10 gallon bucket is too difficult to lift then use smaller buckets to scoop from your big bucket down into the well (make sure you’re wearing your gloves!) Try to pour the liquid in a circular motion to promote as much mixing as possible.

      Well Disinfection

      Step 5  - Circulate the disinfecting chlorine in a hose loop

      Now that the chlorine is in the well, it is time to circulate it around so that the whole well gets disinfected.

      Connect one end of a hose to a nearby spigot that draws from your well. Drop the other end of this hose down your well casing. Turn on the water at the spigot. You’ve just created a circular loop: well water goes from the well to your spigot, through the hose, and back into the well.

      After 15 minutes of circulating the well water, you should smell a rather strong chlorine odor and perhaps see the water changing color. Once you notice the smell, you can turn off the spigot and remove the hose.

      Well disinfection


      Step 6 - Run your disinfectant solution throughout your system

      First, be sure that you have disconnected or bypassed water filters and other chlorine sensitive equipment throughout the house.

      To run disinfectant through your system:

      1. Go to every faucet around the house, one by one, and run your water until you can smell chlorine coming out of the faucet. As soon as you are sure that the chlorine disinfectant is coming out of the faucet, you can turn it off and head to the next one.
      2. Go to every toilet around the house and flush it.
      3. Go to your water heater tank and drain it let it refill with the chlorine shocked water.

      Well Disinfection

      If at any point while you are running faucets you are unable to detect the smell of chlorine, go back to the well and add an additional half gallon of chlorine bleach to 10 gallons of water and repeat Step 4.

      Step 7 - Let it be

      Once you’ve run your disinfectant chlorine solution to every faucet in the house (and confirmed the smell of chlorine), then you are ready for the long wait. We suggest letting the chlorine stand in your pipes and well for at least 8 hours. 12 hours is preferable.

      During this time, make sure that nobody uses any of the water in your house for anything. It will be dangerous to drink, and harmful if your skin touches it. Make sure you have water for people and animals.

      Make sure you turn off automatic sprinklers too because high chlorine concentrations are not good for your plants.

      Step 8 - Flush it out

      Once you’ve waited 8-12 hours before using the water in your home, we can assume that any bacteria in the system has been killed. It is now time to dump out all of your chlorine water from the system.

      Head outside and run your water out of the lines from an available spigot, preferably one with a hose. Dispose of this water away from any plants. Do not drain this water into your septic system.

      Keep the water running until you no longer smell any chlorine. This may take twenty minutes or more. You can also flush all of the faucets around the house for a few minutes so that they no longer smell of chlorine.

      Step 9 - Test your water to make sure treatment worked!

      After one week we suggest you perform another
      bacterial water test to confirm that your chlorine shock treatment has been successful.

      After two months we suggest running one more test to make sure your water has not been recontaminated. If you find re-contamination, there may be another problem causing bacterial contamination.

      Test your water with Tap Score

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      About The Author


      Kate leads operational strategy as COO at Tap Score and SimpleLab. She oversees daily, as well as long-term logistics for tens of thousands of environmental samples across hundreds of certified laboratories. However, she started her environmental testing career by way of scientific blog writing at Tap Score and it continues to be one of her favorite aspects of the business. Outside of Tap Score, Kate loves making homemade pasta, floral arranging, and singing along to Dolly Parton tunes.
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