How To Shock Chlorinate A Well To Kill Coliform Bacteria And Odors

A common concern for homeowners with well water is how to properly disinfect their system, especially after receiving a positive test result for coliform bacteria.

Coliform bacteria in your well or plumbing system may indicate contamination from surface water, septic tank leakage, or inadequate disinfection after drilling or recent maintenance. This can also mean harmful bacteria and viruses may be present. In addition to health risks, other nuisance bacteria—such as iron and sulfur bacteria—can produce foul tastes, odors, and slime, and even clog pumps and plumbing.

Shock chlorination is a common method used to disinfect wells by adding chlorine bleach to kill bacteria and sanitize the system. In this guide, we’ll walk you through how to shock chlorinate a well safely and effectively.

Shock Chlorinate & Sanitize a Well & Home Piping System Whenever:

1. A new well has been constructed
2. Anytime a well is opened for repairs
3. Floodwater has entered a well
4. A new holding tank, pump, or pressure tank has been installed
5. A new pipeline or other piping or plumbing work has been done
6. Tests indicate the presence of coliform bacteria
7. Odors or slime caused by iron or sulfur bacteria are present

How To Shock Chlorinate and Sanitize Wells With Chlorine To Kill Bacteria

It is important to periodically monitor your well for contamination. The EPA recommends testing private water supplies annually for coliform bacteria to detect problems early.

A positive test indicates the likely presence of disease-causing bacteria and viruses, possibly from surface water influence, septic leaks, or improper disinfection after drilling or servicing.

While iron and sulfur bacteria are not health threats, they can cause odors, tastes, and clogging in pumps and water systems.

Shock chlorination can eliminate these harmful bacteria and nuisance organisms, causing bad smells and slime.

You can test for bacteria using a home coliform test kit or by sending a sample to a licensed lab.

CAUTION: Shock chlorination may temporarily discolor water and loosen iron and sediment, which can damage pipes and fixtures. Avoid running such water through water softeners, heaters, or filters.

If unsure or if the well is hard to access, contact a licensed well driller or pump contractor for professional chlorination.

How to Shock Chlorinate a Well: Which Type of Bleach To Use

The best way to shock chlorinate and sanitize wells is to use a combination of dry pellets and dry chlorine granules mixed with water. The dry pellets drop down past the pump and ensure the entire well is sanitized.

In addition, liquid bleach made from potable water grade powdered bleach is poured into the well and then recirculated until the chlorinated water has made its way through the well pipe, pressure tank, and pipes in the house if desired.

You can use regular household bleach (non-perfumed type) that contains 5.25 percent sodium hypochlorite, which kills bacteria and certain viruses. Laundry bleach can contain contaminants such as benzene and heavy metals, so only use it as a last resort if you can not find the powdered bleach and pellets.

You can also use pool chlorine, which is 10% to 12% sodium hypochlorite and twice as strong as household bleach. Do not use pool pellets, which are not designed for potable water.

Note of Caution:

Shock chlorinating a well or piping system may loosen up the scale, iron deposits, and other materials, which can clog fixtures, appliances, and valves in the piping system.

Care should be taken when flushing the piping, and all aerators removed to prevent clogging. In some extreme cases of corroded piping, the piping may fail and start to leak after this procedure. Chlorination will not remove nitrate or other contaminants.

How to Shock Chlorinate Sanitize Wells Using Dry Pellets or Powdered Bleach?

The dry pellet method (70% calcium hypochlorite) can be used for well, storage tanks, or cistern sanitation. The number of tablets and granules used will depend on the amount of water in the system to be sanitized. Half of the total treatment will be completed with chlorine pellets, and the other half will be completed with granular chlorine slurry.

A 100-ppm chlorine concentration is ideal for sanitizing a well. To produce a 100 PPM chlorine concentration, use 2 oz. sanitizer pellets or granules for every 100 gallons of water in the system. (2oz. granules = 70 Pellets) If the water has a high iron or sulfur content more chlorine may be needed to achieve 100-ppm chlorine residual.

Instructions

1. Bypass the water softener, other filters, or purification equipment. Clean the well house, spring house, or storage tank by removing debris and scrubbing interior surfaces with a strong chlorine solution (½ gallon household bleach or 0.2 oz dry bleach granules per 5 gallons of water). Pump out any suspended solids if possible.
2. Remove the well inspection plug or cap carefully. Measure water depth if possible and use the table below to determine the sanitizer amount. If unsure, seek professional help.

3. Mix granules in 5 gallons of water (add product to water, not water to product) and pour into the well. Drop tablets into the well if applicable.
4. Circulate the water by connecting a garden hose to an outdoor sillcock after the pressure tank and running water back into the well for about 15 minutes until a strong chlorine odor is detected. If not, add more bleach and repeat.
5. Let the chlorinated water stand for at least 6 hours, preferably overnight. Then flush outdoor faucets until no chlorine smell remains, followed by indoor faucets.

Do not discharge high chlorine water into septic systems or onto lawns.

Note: Chlorine may cause colored water and loosen iron or organic material that can clog pumps. Do not continue pumping if the water flow stops. Chlorine should not remain in the system more than 36 hours.

6. Return equipment to service.
7. After 6 to 12 hours, safely discharge chlorinated water away from plants and water bodies. Remaining household plumbing water can be discharged into the septic system.
8. Test the water 2 to 3 weeks after treatment. If problems persist, consult a water professional.

(If you want to read more about Chlorinate Sanitize Wells, check out this post)

Shock Chlorinate With Liquid Chlorine Bleach

1. Clean the well house, spring house, or storage tank by removing debris and scrubbing interior surfaces with a strong chlorine solution (½ gallon household bleach per 5 gallons of water).
2. Determine the amount of chlorine needed using the chart below. If unsure of well depth, contact your well driller.

Well Casing Diameter	Distance From Water Level to Bottom of Well (Water Depth)
	0′ – 50′	50′ – 100′	100 – 200′	200′ – 300′	300′ – 400′	400′ – 500′
4″	8 oz	16 oz	24 oz	1 qt	1 ½ gal.	2 gal.
6″	1 qt	2 qt.	1 ½ gal.	2 gal.	2 ½ gal.	3 gal.
8″– 12″	1 gal.	1 ½ gal.	2 gal.	2 ½ gal.	5 gal.	6 gal.
12″ – 16″	1 gal.	2 gal.	4 gal.	6 gal.	8 gal.	10 gal.
20″ – 24″	2 gal.	6 gal.	10 gal.	14 gal.	18 gal.	22 gal.
30″ – 36″	6 gal.	10 gal.	20 gal.	30 gal.	40 gal.	50 gal.

Use half the amount if using pool chlorine (10-12% sodium hypochlorite).

3. Mix the chlorine with 10 times as much water before pouring down the well.
4. Remove the well cap or air vent carefully and pour the diluted chlorine into the well. If unsure, seek professional help.
5. Protect yourself by wearing safety goggles, rubber gloves, and a chemical-resistant apron.
6. Circulate the chlorinated water by running water from an outdoor faucet back into the well for about 15 minutes until a strong chlorine odor is detected.
7. Open all indoor faucets and outdoor fixtures until the chlorine smell is present.
8. Let the chlorinated water stand in the system for 6 to 12 hours.
9. Flush the system by running an outdoor faucet until the chlorine smell dissipates, then do the same for indoor faucets. Avoid discharging chlorinated water onto lawns or septic systems.
10. Backwash water softeners, flush water heaters, and replace filters as needed.
11. Test the water 2 to 3 weeks after treatment. If bacteria persist, consult a professional.

Well System Diagram

Wells with submersible pumps have pipes that either enter through the top or through the side. Many wells are underground or in vaults in areas with freezing temperatures.

Resources:

• See the EPA resource for home water wells: https://www.epa.gov/safewater/pwells1.html
• Consider a home chlorination system to keep your well water disinfected.
• See all our well water treatment systems

Frequently Asked Questions (FAQs)

1. What precautions should I take before chlorination starts?

If you are not familiar with your well or well construction, or how to shock chlorinate a well, consider hiring a licensed well driller to shock chlorinate.

2. When Can I Use the Water Again?

Make sure to flush 4 well volumes before using the water:

• 4” well diameter has 70 gallons per 100 ft of depth
• 6” well diameter has 150 gallons per 100 ft of depth
• 8” well diameter has 260 gallons per 100 ft of depth

Wait for one to two weeks after shock chlorinating the water supply system and then retest for total coliform and E. coli bacteria.

If the test results show the absence of coliform bacteria, the water is safe to drink.

However, if test results show the presence of coliform bacteria, the source(s) of contamination should be identified and eliminated through a licensed well driller/contractor, or a continuous disinfection treatment system should be installed.

3. What Type of Chlorine Bleach Should Be Used?

For best results, use powdered bleach or pellets that are certified for drinking water. However, it is also OK to use unscented household chlorine bleach with at least 5% sodium hypochlorite found in supermarkets.