How To Shock a Well (Step-By-Step Chlorination Guide)

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How To Shock A Well

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.

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.

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

NSF and FDA Certified Calcium Hypochlorite
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

Turn off the power to your well pump. Also, turn off the water to any irrigation systems. If you have a bypass valve on your water filter or softener, turn those on now too. Remove any other filters or appliances that cannot be exposed to bleach.

2. Turn Off Well Pump Power

Switch the electrical power to the pump to the OFF position. For added safety, use the lockout hasp if your circuit breaker box has one to keep the breaker from being turned on.

3. Remove Well Cap

Remove the cap from the well and gently move the wires and connector caps out of the way so they do not get wet later in the process. If your well has a plumbing vent, make sure NOT to remove the compression bolts from the well seal.

4. Inspect Well Area

Inspect the area and remove any debris. It is critical at this point to observe any damaged wires, well casings, or seals so that groundwater cannot leach into your well water supply.

5. Add Chlorine Solution To Well

Add the appropriate amount of chlorine. The type of well and water composition will determine the amount of chlorine solution required to adequately disinfect the water system. The Environmental Protection Agency (EPA) recommends using 50 mg/l for a water system and leaving it in the system for twelve hours. Although, this can be increased to up to 200 mg/L if contamination continues. Note that using a bleach concentration that is greater than 200 ppm will reduce the disinfection effectiveness and potentially damage your plumbing.

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

Then, take your garden hose and attach it to the spigot at the base of the pressure tank or connect it to an outside spigot that does not run through your water treatment system.

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

Turn on every faucet in your home in order to draw the disinfectant through your plumbing system. This includes hot and cold water, showers, baths, and outside spigots. Once you can smell chlorine in the water coming through the fixtures, turn it off. Note that re-dosing may be necessary to fully distribute the chlorine solution throughout the system, particularly if you have a shallow well. If you fail to get chlorine in the correct concentration through all of the water lines, some bacteria could survive and spread through your entire water system.

8. Let The Disinfection Solution Sit

Now that the chlorine solution has spread throughout your plumbing system, you need to let it sit so the disinfection process works. Place signs or cover the fixtures so nobody used the water while the treatment is taking place.

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

Once there has been sufficient contact time, you need to flush the well. Do this by running your garden hose to a dry location that is not near a septic system, plants, open water, or other areas that could be damaged. The water may appear brown or contain sediment. Be sure to keep flushing until the chlorine smell is gone. This may take as little as 30 minutes, or over the course of several days to completely flush the chlorine and sediment. If you have chlorine test strips, check the chlorination levels to ensure it is safe.

10. Turn Back On Appropriate Areas

If you turned the bypass valve on your water filter or softener, turn those back in service now. Place back any filters or appliances that could not be exposed to bleach. Also, turn on the water to any irrigation systems.

11. Test Your Well Water

Test the water for total coliform bacteria and chlorine to make sure it is negative.

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 Diameter8 Inch Diameter36 Inch Diameter48 Inch Diameter
2030 Gallons51 Gallons1,060 Gallons1,880 Gallons
200293 Gallons512 Gallons
400588 Gallons1,044 Gallons
600881 Gallons1,566 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 VolumeLiquid ChlorineCalcium Hypochlorite Pellets
10 mg/L100 Gallons1/4 Cup5 Pellets
10 mg/L500 Gallons1 Cup30 Pellets
10 mg/L1,000 Gallons2 Cups60 Pellets
50 mg/L100 Gallons1 Cup30 Pellets
50 mg/L500 Gallons4 Cups155 Pellets
50 mg/L1,000 Gallons1/2 Gallon315 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

FAQs For Shock Chlorination

Can you use household bleach to shock a well?

It is not recommended to use regular unscented bleach to perform a shock treatment. Despite popular belief, swimming pool chlorine or household bleach is not specifically designed for this use. Bleach and pool chlorine do not effectively target the contaminated areas and can leave behind odors and traces amounts of various elements, including heavy metals. It is therefore recommended to use a specialized well chlorination kit that is FDA-approved.

What happens if you use too much bleach to shock a well?

If you use a chlorine concentration over 200 ppm to shock your well it will not effectively disinfect the system. Not only will it not kill iron or total coliform bacteria, but it can also damage plumbing due to the alkalinity.

How long does it take for the chlorine to leave the plumbing?

It can take between 30 minutes to 24 hours for the chlorine solution to be completely flushed from the system. You can go by the smell and discoloration of the water. Note that the bleach needs to sit within the plumbing and fixtures for at least 6 hours to obtain the necessary contact time before flushing it out.

Is the water safe to drink after shocking a well?

Yes, well water is safe to drink after shocking a well. You need to test the water for chlorine and bacteria to make sure the chlorine is below 4 ppm and that the bacteria have been killed. Then it is safe for drinking, but having some type of carbon filter or reverse osmosis is very desirable. 

How long do I need to wait to shower after shocking a well?

You should wait 24 hours after shocking a well before bathing or showering in the water or until you cannot smell any chlorine. Use chlorine test strips to ensure the chlorination levels are at an acceptable level. If you have sensitive skin, you may want to add an extra time buffer to make sure the water is acceptable.

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