Mark Timmons 
Sourcing water from a private well means that you are solely responsible for the quality of your water supply. Shock chlorination is an effective treatment for the safety of your well water, and it can be performed by any homeowner. In this guide, I will walk you through how to shock a well with chlorine solution to kill lingering bacteria.
No matter what type of well you have, I’ll share my experience on when to shock your well, how much chlorine to use, why using household bleach is not ideal, and the proper protocol to ensure it’s safe.
Key Takeaways:
- Shock chlorination disinfection should be done once per year to kill harmful well water bacteria
- The best type of disinfectant is an NSF and FDA Certified Calcium Hypochlorite solution
- It is not recommended to use household chlorine bleach because it can contain contaminants that should not be in potable water and is not as effective
- The amount of chlorine solution used depends on the type and depth of your well
- The chlorine solution needs to sit at least 8 hours for optimal contact time before flushing
What Is Shock Chlorination
Shock chlorination is a way of sanitizing wells with chlorine. It is actually the most commonly recommended method of treating wells that have bacterial contamination. It is often considered to be a good idea after your well has been installed, repaired, maintained, or had construction performed on it. The method is also recommended if there has been flooding or some other type of contamination in the area. Shock chlorination works well for the following kinds of bacteria.
- E. Coli
- Fecal Coliform
- Iron Bacteria
- Anaerobic, Sulfur-Reducing Bacteria
However, the method is not a good choice for recurring bacteria issues, such as can occur if your source water is contaminated or if there is a leak from a septic system tank close to your well. These situations will require a different kind of treatment.
How Often Should You Shock Your Well To Kill Bacteria?
Private wells should be treated with a bleach chlorination solution at least once per year to kill harmful bacteria that are harbored. The disinfection process is considered the best practice to maintain well infrastructure, but should not be relied on for recurring bacteria issues. However, if you have tested your water and found that it tested positive for coliform bacteria, it is a good method to use.
There are signs to look for between regular tests that may indicate a problem, in which case you should test your water sooner. Here are some signs that there may be bacterial growth in your well water.
- Laundry Appears Stained: If you have noticed that your white clothes appear to be a light orange shade after being washed, it could mean that your water has bacterial contamination.
- Slime: If you see slime deposits in places where your water tends to sit for a while, such as in the toilet tank or the well cap, it could mean you have an iron bacteria build up.
- Unpleasant Taste or Odor: It is a good idea to test your well water if it has developed an unpleasant taste or odor. The common rotten egg smell could be a sign of sulfate-reducing bacteria.
- Reduced Flow: Iron bacteria in a well will deposit rust throughout your well system over a period of time. This can reduce the flow of water in your system or even cause blockages.
If any of these signs occur, you should have your water tested to see if it has bacterial contamination. Then if you do find contamination, shock chlorination is often a good way to disinfect your well.
Need to test your water? Check out our well water laboratory test kits
Is It Safe To Shock A Well?
Yes, it is not only safe to shock chlorinate a well, but it is recommended to do on a regular basis to kill harmful coliform bacteria. To ensure the drinking water is safe following a disinfection treatment, one needs to make sure the water tests negative for bacteria and chlorine. Do not allow people to use the water until the treatment is completed and confirmed safe for consumption.
The Environmental Protection Agency has set a maximum chlorine level in drinking water of 4 parts per million (PPM). You can use chlorine water test strips following the treatment process to make make sure the chlorine level does not exceed this. The ideal level is between 0.2 – 0.5 ppm. This is the concentration at which microorganisms are effectively treated while not creating unwanted tastes or odors in the drinking water.
It is also critical to test the water for total coliform 2 – 3 weeks after the treatment to make sure any bacteria has not reemerged.
Lastly, have a plan to safely dispose of the chlorinated water that is flushed out. Make sure that you do not dispose of the water directly on any plants or animals. You should also not dispose of the chlorine water in a pond or stream as it will hurt aquatic life. You might be able to locate a drain nearby where you could safely dispose of the water.
What Is The Best Type Of Chlorine To Shock Your Well
We suggest using a two-prong approach by dropping large chlorine pellets down the well, and they will find their way to the bottom. Then mix up chlorine hypochlorite in a five-gallon bucket of water and pour it into the well casing. This tends to stay at the top of the well. We will discuss further procedures later in this article.
We recommend using a chlorine shock kit like Well Safe which includes everything you need to effectively disinfect your well.
Well Safe Well Chlorine Shock Kit Best Shock Kit
Will help prevent iron and iron bacteria
Lasts longer than liquid chlorine
Includes pellets and granules for a comprehensive treatment
Calcium Hypochlorite
The best disinfectant is an NSF and FDA Certified Calcium Hypochlorite solution which is much stronger and more deadly to bacteria. We do not recommend using chlorine bleach because chlorine bleach can contain contaminants that should not be in potable water.
Note: You should not use liquid chlorine bleach unless it is NSF and FDA Approved. The problem with bleach is that it is typically 5.25% chlorine or less. Calcium Hypochlorite is typically over 70% and much more effective at sanitizing the well compared to bleach.
Dry Chlorine Pellets (Tablets)
You can also use dry bleach pellets. These are typically either sodium hypochlorite or calcium hypochlorite. The pellets usually have a 70% hypochlorite concentration. When using pellets, they should not contain algaecide, conditioners, fragrances, or stabilizers.
Safety Precautions
Before beginning your shock chlorination treatment, please make note of the following safety precautions:
- Follow the manufacturer’s safety and use directions
- Ensure no one uses the chlorinated water until it is confirmed to be safe from chlorine and bacteria
- Keep children and pets away from the well area during the disinfection process
- Use caution while working with the electrical components within your well
- Use the appropriate eye and skin protection to avoid contact with the bleach
- Mixing bleach can create harmful gases, make sure you have proper ventilation
Make sure to follow the correct protocols to ensure your safety and that of your family, and pets. Not adhering to the provided guidelines can lead to unintended health consequences and potential damage to your well and plumbing.
How To Disinfect A Well Using Chlorine
What you will need:
- Chlorination Kit
- Bacteria Test Kit
- 5-gallon Bucket
- Garden Hose
- Safety Gloves & Goggles
1. Turn Off Appropriate Areas
2. Turn Off Well Pump Power
3. Remove Well Cap
4. Inspect Well Area
5. Add Chlorine Solution To Well
To mix the solution, fill a 5-gallon bucket with water from the system, add the chlorination granules, and pour it into the well casing. Next, pour the pellets into the well.
When the bleach solution is prepared, use a funnel to pour the chlorine solution into the well so it doesn’t contact the well cap or the wires.
6. Circulate Chlorinated Water
Now, you can turn the power to the pump back on and open up the spigot connected to the hose to run for approximately 15 minutes away from the well or septic system until the water runs clear. Turn off the water and place a funnel inside the well. Now place the hose in the funnel and begin recirculating the water for approximately 30 minutes until the smell of chlorine is still not greater than you would smell in pool water. If you have test strips, use them to test the chlorine concentration. When this is complete, turn off the water and the pump electrical switch.
After the entire process is over, be sure to wash off any wires as well as other parts of your well interior, including the pitiless adaptor, because chlorine is quite corrosive and will cause damage to fittings and wiring. With large-diameter dug wells you can scrub the interior walls too. After rinsing the components, turn the breaker back on.
7. Allow Bleach To Enter Plumbing And Fixtures
8. Let The Disinfection Solution Sit
The chlorine solution should sit in the plumbing system for at least 6 hours. It does not hurt, but will only help if you allow the chlorine to sit for 12 – 24 hours for maximum contact time.
9. Flush System
10. Turn Back On Appropriate Areas
11. Test Your Well Water
Important: Follow-up to test your well for bacteria 2 or 3 weeks after the disinfection process. If your water tests positive for total coliform bacteria repeat the disinfection treatment steps. If after several attempts to disinfect the system there is still coliform bacteria present, there is likely a structural issue with your well that needs to be addressed.
How Much Chlorine To Shock A Well?
The concentration of chlorine used to disinfect a well depends on the depth and type of the well. Large-diameter dug wells generally have a depth of fewer than 20 feet. However, gravel or bedrock wells can reach 400 or more feet. The depth of the well can be used if you are not able to calculate the amount of water in the well.
If you purchase the chlorine shock kit, we generally recommend using the entire 8 oz bottle of granules and pellets for the well.
First, use this table to help estimate the volume of water in your well:
| Well Depth (Ft) | 6 Inch Diameter | 8 Inch Diameter | 36 Inch Diameter | 48 Inch Diameter |
| 20 | 30 Gallons | 51 Gallons | 1,060 Gallons | 1,880 Gallons |
| 200 | 293 Gallons | 512 Gallons | – | – |
| 400 | 588 Gallons | 1,044 Gallons | – | – |
| 600 | 881 Gallons | 1,566 Gallons | – | – |
Below are the amounts of chlorine needed, in either pellet or liquid form, for different concentrations given the volume of water. If you have a well that is deeper than 200 feet, solid chlorine pellets are especially ideal because they take longer to dissolve and will sink to the bottom.
Second, use this table to know the proper amount of chlorine to add:
| Target Concentration (mg/L) | Water Volume | Liquid Chlorine | Calcium Hypochlorite Pellets |
| 10 mg/L | 100 Gallons | 1/4 Cup | 5 Pellets |
| 10 mg/L | 500 Gallons | 1 Cup | 30 Pellets |
| 10 mg/L | 1,000 Gallons | 2 Cups | 60 Pellets |
| 50 mg/L | 100 Gallons | 1 Cup | 30 Pellets |
| 50 mg/L | 500 Gallons | 4 Cups | 155 Pellets |
| 50 mg/L | 1,000 Gallons | 1/2 Gallon | 315 Pellets |
These tables are best for disinfecting a well system in an average home. Note that you should also add approximately 50 gallons to account for the water in the tanks and plumbing of your home. If you are only disinfecting the well, you can reduce the amount of disinfectant accordingly. You can increase the concentration if:
- The well has not had a disinfection treatment in several years
- The home is larger than average and has more plumbing
- If you’re disinfecting the well following a flood
