How to Disinfect Your Drinking Water

1. Visually inspect your well and water system and make any repairs.

• Look for and fix any sources of bacterial contamination around your well, such as leaks, un-mortared joints, loose caps, ripped vent screens, etc.
• Watch a video on common problems with wells and how to fix them.

2. Consider testing for nitrate and chloride.

• If nitrate or chloride are in your water, this might mean that a septic system or nearby farm could be the source of contamination.

3. Gather the materials you will need.

• Rubber gloves and eye protection
• Household liquid chlorine bleach that contains no scents or additives
• 5-gallon bucket
• Small brush
• Garden hose
• Measuring cup

4. Find out the depth and dimensions of your well.

• For drilled wells, most have an “ID” tag attached to the casing. This number can be used to search this database to find the depth of the well and static water level. If you do not know the depth of the well, and there is no well ID tag, contact the person or company who drilled your well or reach out to a local well driller.
• For dug wells, you will need to know the volume of water stored in the well. If you don’t know the volume, you can calculate it.
  • For a cylindrical well, find the radius (distance from the center to the outer circle) and the depth and use this calculation: volume in gallons = (radius)² (in feet) x 3.1415 x depth (in feet) x 7.5

5. Draw enough water to last for 3 to 5 days.

• The disinfection process, including flushing, can take up to 24 hours. During this process, the water will have high levels of chlorine in it. Make sure you have an alternate source of water to use for drinking, cooking, making baby formula, bathing, showering and laundry. You can use the water for flushing toilets.
• Boil for one minute any water used for drinking, cooking, washing food, brushing teeth, or making ice or baby formula. You can also get or buy water from another safe source. Note: boiling water may concentrate other contaminants, like nitrate, in your well. Only boil your water if you know there are no other contaminants in your water. Learn more about testing for drinking water contaminants.

6. Flush your well.

• Turn on an outside spigot and flush approximately one volume of the well. Be careful not to pump the well dry, which could damage it and cause your water to become contaminated.
• Do not drain the water into your septic system since it could overload it.
• Test your water for bacteria again since flushing can sometimes get rid of it.

Download or print the step-by-step guide to disinfecting your well

You will be adding chlorine bleach directly to your well. Chlorinated water will then travel throughout the plumbing and faucets in your home.

1. Disconnect or bypass any water treatment devices, like water softeners or reverse osmosis units, since bleach can damage them. You will need to disinfect these devices separately according to the manufacturer’s instructions.
2. Gather materials needed: rubber gloves, eye protection, household chlorine bleach that contains no scents or additives, 5-gallon bucket, small brush, garden hose, and a measuring cup. Wear rubber gloves and eye protection whenever you are working with bleach.
3. Keep children and pets away from the area, especially from bleach and chlorinated water. Turn off power to the pump.
4. Remove the well cap. Inspect and fix any exposed wires. You can turn power to the pump back on, but do not get the wires wet.
5. Mix 1 cup of bleach with a half-gallon of water in the bucket. Use this water to clean the well cap and sides of a dug well using the scrub brush. Discard the water away from your septic system and any streams.
6. Calculate the amount of bleach needed by using the chlorine calculator or use a rough estimate of a 1/2 cup of bleach for every 10 feet of depth for a standard 6-inch diameter drilled well, or use 1 cup of bleach for per 25 gallons of water storage for dug wells.
   • The goal is for the water to reach a chlorine concentration between 100 to 200 ppm. How you estimate the volume of  water in your well or which method you use may result in slightly different concentrations, between 100 to 200 ppm.
7. Carefully pour the bleach into the well.
8. Use the garden hose to run water into the well to mix and circulate the bleach. Run the water along the well casing or sides of the dug well. Do this for at least 15 minutes and up to 1 hour.
9. Reseal the well and (if applicable) install a new gasket if it is brittle or missing.
10. Go to the faucet inside your home that is farthest from the well and run the cold water until you smell bleach. Turn the tap off, then do the same with the hot water. Repeat this step for all faucets, shower and baths, toilets, and outside spigots. Remove any screens on your faucets as they can become clogged by debris dislodged during the disinfection process.
11. Check the manufacturer's instructions before running the chlorinated water into your clothes washer, dishwasher or refrigerator water filtration system.
12. Leave the chlorinated water in the plumbing for 8 to 12 hours to give the chlorine time to disinfect your system. It is important to let the water sit for at least 8 hours. The chlorinated water needs to touch the well and each area of the plumbing for an extended period of time in order for it to work. This will make sure bacteria is eliminated. However, allowing water to sit in pipes much longer than 12 hours may result in corrosion of your plumbing.  
13. After at least 8 hours, flush the system until you no longer smell bleach. Start with an outside spigot. Connect a garden hose so it drains onto a gravel driveway or brushy area away from your septic system and any streams. Flushing large volumes of chlorinated water into your septic system may damage it. You may want to run the water at less than full flow or turn the tap off periodically to allow the well to recharge so it does not run dry.
14. Flush the taps inside your home by running both the hot and cold faucets until you no longer smell bleach.
15. Remove, clean, then replace any screens on your faucets as they can become clogged by debris dislodged during the disinfection process.
16. Retest your water 2 to 3 days after the chlorine smell is gone. Order the bacteria test (Kit A) from the Health Department Lab. It is best to thoroughly sanitize the faucet head using rubbing alcohol and a cotton swab before colleting the sample. 

17. Continue to either boil your water or get water from a safe source until no bacteria are detected. 

    Note: Water may be cloudy, discolored, or have a lot of sediment immediately after shocking a well. This should go away within a few days after flushing the chlorinated water out of the system. 

If problems continue

You may need to:

• Scrub and clean the well casing to remove bacteria that can build up on the well casing and borehole walls.  
• Disinfect with a higher concentration of chlorine, up to 200 ppm, or double the chlorine calculator’s output.  
• Use chlorine indictor strips to check the chlorine concentration at an indoor faucet. This can help make sure enough chlorine is reaching the faucet and other plumbing components.  
• Get your well professionally inspected by a well contractor. They have the equipment to clean the well or run a camera down to find cracks or other issues. This is generally recommended every ten years. 

The well casing may also need a thorough scrubbing or cleaning to remove bacteria that can build up on the well casing and borehole walls. Consider getting the well professionally inspected by a well contractor. They have the equipment to clean the well or run a camera down to find cracks or other issues. This is generally recommended every ten years.

Consider permanent treatment for your water supply if you have disinfected several times and a well inspection does not find the cause of the contamination. Make sure any treatment device is certified by NSF or ANSI.

Permanent treatment options include:

• Ultraviolet (UV) light treatment that meets NSF/ANSI Standard 55
• A filter that meets NSF/ANSI Standard 53 and is 1 micron (absolute), which is approved to remove disease-causing bacteria
• A chlorinator, which injects exact amounts of chlorine into your plumbing system when the water is being pumped to the home.

Learn more about water treatment

Using the Chlorine Concentration Calculator, enter in the:

1. Depth of your well
2. Depth to the water table
3. Diameter of your well

Be sure to check the concentration of the bleach you use. The calculator will give you the amount of chlorine to use for 6% and 8.25% solutions to provide a 100 ppm chlorine concentration in the water. Many household bleach products are concentrated at 8.25%. Remember to use ordinary household bleach without any added detergents or additives.

Use the Chlorine Concentration Calculator

This video will help you understand your well water system, how to calculate the volume of bleach needed for disinfection, and how to safely apply it. This video shows how to calculate a 200 ppm chlorine solution.

1. Visually inspect your spring system and make any repairs.

• Look for and fix any sources of bacterial contamination in and around your spring, such as visible cracks, blockages at the inlet or outlet, debris inside the spring box, loose caps or fittings, etc.

2. Consider testing for nitrate and chloride.

• If nitrate or chloride are in your water, this means a septic system or nearby farm could be the source of contamination.

3. Gather the materials you will need.

• Rubber gloves and eye protection
• Household liquid chlorine bleach that contains no scents or additives
• Fast-dissolving 65-70% calcium hypochlorite pellets with no algaecides, chlorine stabilizers/conditioners, acids, or other disinfectants (available at pool supply or hardware stores)
• 5-gallon bucket
• Small brush
• Garden hose
• Measuring cup

4. Draw enough water to last for 3 to 5 days.

• Boil for one minute any water used for drinking, cooking, washing food, brushing teeth, or making ice or baby formula. You can also get or buy water from another safe source. Note: boiling water may concentrate other contaminants, like nitrate, in your spring. Only boil your water if you know there are no other contaminants in your water. Learn more about testing for drinking water contaminants.

5. Flush your system if the water appears cloudy or full of sediment.

• Turn on an outside spigot and flush water until it begins to run clear. Be careful not to pump the spring dry, which could damage it and cause your water to become contaminated.

Download or print the step-by-step guide to disinfecting your spring

You will be adding calcium hypochlorite pellets and chlorine directly to your spring. Chlorinated water will then travel throughout the plumbing and faucets in your home.

1. Disconnect or bypass any water treatment devices, like water softeners or reverse osmosis units, since bleach can damage them. You will need to disinfect these devices separately according to the manufacturer’s instructions.
2. Gather materials needed: rubber gloves, eye protection, household chlorine bleach that contains no scents or additives, calcium hypochlorite pellets (with no algaecides, chlorine stabilizers/conditioners, acids, or other disinfectants), 5-gallon bucket, small brush, garden hose, and a measuring cup. Wear rubber gloves and eye protection whenever you are working with bleach.
3. Keep children and pets away from the area, especially from bleach and chlorinated water. If pump-operated, turn off power to the pump.
4. Calculate the amount of disinfectant you will need for your spring. Use fast-dissolving 65-70% calcium hypochlorite solid pellets (with no additives). Estimate the volume of water in the spring box. You will need 3 ounces of pellets for every 100 gallons of water. For many spring boxes, 2 feet in depth is 100 gallons of water, but you may need to modify this calculation based on your spring. One cubic foot of water is equal to 7.5 gallons. The goal is for the water to reach a chlorine concentration between 100 and 200 ppm.
5. Flush and drain the spring box and remove debris and sediment. Scrub the interior of the spring box with a strong chlorine solution (1/2 cup of plain, unscented, liquid laundry bleach mixed in 5 gallons of water.
6. Allow the spring box to fill with fresh water. Add 3 ounces (85 grams) of the calcium hypochlorite pellets for every 100 gallons of water in the spring. Keep the overflow outlet open.
7. Go to the faucet inside your home that is farthest from the spring and run the cold water until you smell bleach. Turn the tap off, then do the same with the hot water. Repeat this step for all faucets, shower and baths, toilets, and outside spigots. Remove any screens on your faucets as they can become clogged by debris dislodged during the disinfection process.
8. Leave the chlorinated water in the plumbing for 8 to 12 hours to give the chlorine time to disinfect your system. If the flow rate is too high to keep the chlorine solution for 8 to 12 hours, use a tank to feed the chlorine solution into the spring box continuously for at least eight hours. It is important to let the water sit for at least 8 hours because the chlorinated water needs to touch the well and plumbing for an extended period of time in order to work. This will make sure bacteria is eliminated. However, allowing water to sit in pipes much longer than 12 hours may result in corrosion of your plumbing.
9. After 8 to 12 hours, flush the system until you no longer smell bleach. Start with an outside spigot. Connect a garden hose so it drains onto a gravel driveway or brushy area away from your septic system and any streams. Flushing large volumes of chlorinated water into your septic system may damage it. You may want to run the water at less than full flow or turn the tap off periodically to allow the spring to recharge so it does not run dry.
10. Flush the taps inside your home by running both the hot and cold faucets until you no longer smell bleach.
11. Remove, clean, then replace any screens on your faucets as they can become clogged by debris dislodged during the disinfection process.
12. It is best to thoroughly sanitize the faucet head using rubbing alcohol and a cotton swab before collecting a sample. Retest your water 2 to 3 days after the chlorine smell is gone. Order the bacteria test (Kit A) from the Health Department Lab. You may want to retest 2 to 4 weeks later to ensure that bacteria do not continue to enter the spring.
13. Continue to either boil your water or get water from a safe source until no bacteria are detected.

If problems continue

Springs are susceptible to bacteria contamination.

You may need to:

• Disinfect with a higher concentration of chlorine, up to 200 ppm.  
• Use chlorine indicator strips to check the chlorine concentration at an indoor faucet. This can help make sure enough chlorine is reaching the faucet and other plumbing components.  

• Mix the water with liquid chlorine bleach as shown in the Table of Chlorine Dosages below.
• Mix the water and chlorine thoroughly and then let it stand for 2 to 3 hours. Store the water in a human-made covered reservoir, tank or other sealed clean container to protect against recontamination.
• Spring, pond, stream or well water that is turbid (cloudy or containing particles) must be boiled for five minutes before using it for drinking, washing fruits or vegetables, and making ice, juice or baby formula.
• Chlorine or any other disinfectant will not work well when water is turbid. The chlorine cannot always go through the suspended particles and may not get rid of organisms that cause sickness.

* Household laundry bleach (5.25% chlorine concentration)