What to Do about Coliform Bacteria in Well Water (2023)

Coliform bacteria are a large group of many kinds of bacteria, including fecal coliform bacteria, which occur naturally in the intestines of warm-blooded animals. The group also includes non-fecal coliform bacteria.

One species of fecal coliform bacteria isEscherichia coli. IfE. colior other fecal coliform bacteria are in well water, the water has come into contact with human or animal waste and could cause disease.

People who drink water from a private well should have the water tested at least once a year to make sure that it is safe to drink. If you receive a positive test result (present) for total coliform or coliform bacteria, follow the guidelines below.

1. Retest to confirm contamination.

If you have received a positive test result (present) for total coliform or coliform bacteria, collect another water sample, and have it screened or tested for fecal coliform bacteria orE. coli. Although the coliform bacteria can indicate something may be wrong with the well, the first water sample that was screened or tested may have been contaminated during the collection process.

Coliform bacteria are common and do not necessarily indicate that the water has come into contact with human or animal waste. But the presence of fecal coliform orE. coliin water definitely indicates contamination by contact with human or animal waste.

When you have the water screened or tested again, test it specifically for fecal coliform orE. coli, and take these steps to get an accurate result:

  • Carefully follow the laboratory’s instructions for collecting a water sample.
  • Before collecting water, remove any aerator, filter, or hose from the faucet.
  • Wash your hands, and do not touch the inside of the container or the cap of the container.
  • Use the faucet that is as close to the well as possible, or use water from a different faucet than you used for the first sample.

2. Do not drink the water.

Use bottled water for drinking and cooking until you receive the results from the second water screen or test. If bottled water is unavailable, boil the water used for drinking, cooking, and brushing your teeth to make it safe.

(Video) How do you get rid of coliform bacteria in water?

For information on how to disinfect small amounts of water, seeEmergency Disinfection of Drinking Waterby the U.S. Environmental Protection Agency athttps://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water.

3. Find the source, and fix the problem.

Possible causes of contamination include a faulty wellhead or improper well construction; a well that is shallow or is near a body of surface water (a pond, lake, stream, or river); an old, unused, or abandoned well; a septic system; or another concentrated source of contamination nearby.

Source: Faulty wellhead or improper well construction

A diagram of a properly completed well is shown inFigure 1. For other completion methods authorized in Mississippi, see theWell Contractors/Drillers/Pump Installers Regulationspublication (pages 16–21) by the Mississippi Department of Environmental Quality athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).

Check the well for signs of faulty seals, and inspect the surrounding area:

  • Is water standing near the well?
  • Is the well cap sealed properly?
  • Are there problems with the annular seal1between the well casing and the soil?

It is usually most efficient to have a licensed well driller check the well and fix the problem. A list of licensed well drillers in Mississippi may be found athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).

What to Do about Coliform Bacteria in Well Water (1)

1The annular seal is the material between the borehole wall and the casing, usually placed near the land surface. It is designed to keep surface water and other potential contamination out of the well. Materials commonly used include bentonite (a sticky clay) and neat cement grout (cement and water with no sand). Source:http://mbmggwic.mtech.edu/sqlserver/v11/help/welldesign.asp.

Source: The well is shallow and/or near a body of surface water

The well may be shallow (especially hand-dug wells), or it may be drawing water from a river or stream that is contaminating the well water. If this is the case:

  • decontaminate the water using a distillation, ozone, ultraviolent (UV), or continuous-chlorination treatment method, or
  • find another source of water, such as by drilling a deeper well, using bottled water, or connecting with a community water system.

Source: Old, unused, or abandoned wells nearby

Old wells that have not been plugged may be acting as a conduit for contamination.

(Video) Dirty Water Week:Total coliform bacteria test results

  • Determine whether old water wells are near your active well.
  • If so, follow the guidelines inWell Contractors/Drillers/Pump Installers Regulations(pages 23–25) athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).
  • A better option may be to work with a licensed well driller to have the well(s) plugged properly.

Source: A septic system near the water well

A septic tank should be a minimum of 50 feet from the water well. Septic drainfields or spray fields should be at least 100 feet from the well.

  • Maintain or pump your septic system as needed. SeeManaging Household Wastewater: An Environmental Self-Assessment for Homes with Private Wells, available athttp://extension.msstate.edu/publications/publications/managing-household-wastewater-environmental-self-assessment-for-homes.
  • Repair the tank or drainfield as needed to prevent leaks that contribute bacteria and nutrients into your drinking water.

Source: Other concentrated contaminants near the well

Animal waste is a common source of bacteria in water wells. A possible source is runoff from feedlots, pastures, dog runs, or any other land containing animal waste.

  • Check the well area for sources of animal waste.
  • Move the source(s) if possible.

If you cannot move the source, make sure that the well components are in good condition, and inspect the wellhead regularly.

4. Disinfect the well.

After you have addressed the causes of bacterial contamination, have the well disinfected by shock chlorination. To reduce your risk of exposure to hazardous chemicals and to protect the well components, have a licensed well driller/pump installer disinfect the well. You do not have to wait until bacteria is present to have your well disinfected. It is recommended that wells be disinfected once per year.

The Mississippi Department of Environmental Quality has posted lists of licensed well contractors/drillers/pump installers in Mississippi athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).

If you shock-chlorinate the well yourself, follow the instructions in the publicationPrivate Well Disinfectionathttps://msdh.ms.gov/msdhsite/_static/30,1937,76,762.html. Also review the owner’s manual or manufacturer’s literature to avoid damaging the components of your well or water-treatment system.

5. Retest the water.

Have the well water retested before drinking it untreated. After any negative test results, retest the water in 6 months to a year and at least annually.

For More Information

Emergency Disinfection of Drinking Water.Environmental Protection Agency. June 2020. Office of Water 4606-M, EPA 816-F-15-003. Available athttps://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water.

(Video) Bacteria in your Well Water

List of licensed well contractors/drillers/pump installers in Mississippi. Mississippi Department of Environmental Quality. Available athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/ (listed under Related Links).

Managing Household Wastewater: An Environmental Self-Assessment for Homes with Private Wells.Mississippi State University Extension ServicePublication 1869. Available athttp://extension.msstate.edu/publications/publications/managing-household-wastewater-environmental-self-assessment-for-homes.

Private Well Disinfection.Mississippi State Department of Health. Available athttps://msdh.ms.gov/msdhsite/_static/30,1937,76,762.html.

Mississippi State University Extension Service county offices:http://extension.msstate.edu/county-offices.

Guidelines for Securing the Services of a Water Well Driller. Mississippi Department of Environmental Quality. Available athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).

Homeowner’s Water Well Checklist. Mississippi Department of Environmental Quality. Available athttps://www.mdeq.ms.gov/permits/water-well-drillers/forms/(listed under Related Links).

Mississippi Well Owner Network:http://extension.msstate.edu/natural-resources/water/mswon.

What to Do about Coliform Bacteria in Well Water. Drew M. Gholson, Diane E. Boellstorff, and Mark L. McFarland. 2014. Texas A&M AgriLife Extension.http://twon.tamu.edu/media/619641/what-to-do-about-coliform-in-well-water.pdf.

(Video) Total Coliforms

Private Well Disinfection. Mississippi State University Extension ServicePublication 3398. Available at http://extension.msstate.edu/publications/disinfecting-water-well-through-shock-chlorination.

Publication 3078(POD-09-20)

ByJason R. Barrett, PhD, Assistant Extension Professor, Water Resources Institute;Drew M. Gholson, PhD, Assistant Professor, Delta Research and Extension Center; andDiane E. Boellstorff, PhD, Associate Professor and Extension Water Resource Specialist, Texas A&M AgriLife Extension Service.

Copyright 2020 by Mississippi State University. All rights reserved. This publication may be copied and distributed without alteration for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service.

Produced by Agricultural Communications.

Mississippi State University is an equal opportunity institution. Discrimination in university employment, programs, or activities based on race, color, ethnicity, sex, pregnancy, religion, national origin, disability, age, sexual orientation, genetic information, status as a U.S. veteran, or any other status protected by applicable law is prohibited. Questions about equal opportunity programs or compliance should be directed to the Office of Compliance and Integrity, 56 Morgan Avenue, P.O. 6044, Mississippi State, MS 39762, (662) 325-5839.

Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. GARY B. JACKSON, Director


How do you get rid of coliform bacteria in well water? ›

You can use regular household bleach to disinfect a well. The chlorine in the bleach will destroy bacteria.

Can I shower if my well has coliform? ›

coli are present, the well may be contaminated by human or animal feces. Wells can become contaminated with bacteria when work is done on the well, if the well was not built properly, or if there are nearby sources of animal or human waste. You can use water for bathing.

How much coliform is acceptable in well water? ›

The Maximum Contaminant Level (MCL) for bacteria in drinking water is zero total coliform colonies per 100 milliliters of water as established by the EPA. The total coliform test is the basic yardstick for determining the biological quality in a water supply.

Can you drink well water with coliform bacteria? ›

If total coliforms (E. coli) are in your well water, you may have diarrhea, cramps, nausea, headaches or other symptoms. Infants, young children and people with compromised immune systems are at a higher risk.

Does water softener remove coliform bacteria? ›

A water softener does not remove bacteria from your water supply. To remove bacteria from your water supply you will want a whole house water filter.

Does a water softener remove coliform? ›

Many people install a water softener because they have hard water issues caused by an elevated concentration of calcium, magnesium, and perhaps iron in their water. Some people believe that a water softener can remove other contaminants such as microorganisms, but this is simply not true.

How long does it take to treat coliform in well water? ›

After disinfection of a well, you should retest your water for total coliform bacteria approximately 10 to 14 days later. If no coliform bacteria are present, wait an additional two to three months and have the water tested again.

How long does coliform last? ›

How long does it last? Symptoms usually last 5 to 10 days. People with mild symptoms usually recover on their own without treatment. Antibiotics are not helpful for treating E.

What does a positive coliform test indicate? ›

What does a positive coliform test result mean? A positive coliform test means possible contamination and a risk of waterborne disease. A positive test for total coliforms always requires more tests for fecal coliforms or E. coli.

What is considered a high coliform count? ›

Sometimes, coliform bacteria results are reported as "TNTC" (too numerous to count) or "confluent." TNTC means that the bacteria concentration was so high that it could not be counted (generally higher than 200 colonies per 100 mL).

How do you chlorinate a well for coliforms? ›

Use ordinary liquid laundry bleach to shock chlorinate the water system. Determine how much bleach to use, then pour the bleach down the well and circulate it through the whole water distribution system. Wait 6-12 hours for the chlorine to work, then flush the chlorinated water from your well and pipes.

What water temperature kills coliform bacteria? ›

It is also reported that a 99.999% kill of water borne microorganisms can be achieved at 149°F/65°C in five minutes of exposure.

What happens if your well tests positive coliform? ›

What do the Results Mean? If coliform bacteria are present in your drinking water, your risk of contracting a water-borne illness is increased. Although total coliforms can come from sources other than fecal matter, a positive total coliform sample should be considered an indication of pollution in your well.

Why does my well keep testing positive for coliform? ›

Coliform bacteria in a water system are generally either a result of a failure to maintain a “closed” system and/or equipment failure. Visually inspect the system including wells, tanks, chlorinator, etc. Look for areas where soil, leaves, insects, animals, sewage or animal wastes could get into your system.

What does it mean when a water test test positive for coliform? ›

What does a positive coliform test result mean? A positive coliform test means possible contamination and a risk of waterborne disease. A positive test for total coliforms always requires more tests for fecal coliforms or E. coli.

Can you get a false positive coliform test? ›

Sometimes, you can get a false positive for coliform, so a resampling will double check the initial result.

What to do if well water tests positive for bacteria? ›

If there is a source of bacteria reaching your well, chlorinating the system will kill the bacteria in the well but the system will soon be contaminated again. A chlorine solution is the simplest and most effective agent for disinfecting a well, pump, storage tank or piping system.

Can you have coliform in water but no E. coli? ›

Total coliform bacteria (without the presence of E. coli) are generally not considered harmful, but their presence indicates a potential pathway for contamination to enter the drinking water. If you have specific health concerns, you may want to consider seeking an alternate source of water.

What to do if well water test fails? ›

Until you have treated the well or disinfected the water, do not drink it or use it for cooking, cleaning, or washing. While the coliform bacteria in your well may not make you sick, its presence is an indication that your well may have other pathogenic organisms that could bring on serious illness.


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