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Positive Coliform Test on Your Well? What It Means and What to Do

Last updated Reviewed by Sean Mihelich, founder of Save My Well

Transcript

My well water tested positive for coliform, so what can you do? First, read the test card, because two lines on it matter. Line one says coliform, and a high count often means other germs are there too. Scientists found it in about one in three wells they tested. Now look at line two, which tests for E. coli. If that line is positive, it likely means poop got into your well. Next, shock the well, and follow each step. After the shock, test the water again in a week or two. If it comes back, germs may be getting in through a crack or a loose cap. That is the time to call a licensed well contractor to find the leak. Get your well tested at save my well dot com.

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Your well test says coliform positive. Here is what that word means.

Your well test came back positive for coliform. Coliform are germs. Most of them do not hurt people. A few can make you sick.[1] They are a sign. They tell you other germs may be in the water too.[2][3] So do not drink the well water yet.[4]

You are not alone. In one study of 450 wells, about 1 in 3 had coliform.[5]

Step 1: Stop drinking the well water

Drink bottled water for now.[4] No bottled water? Call your health department or a well pro before you drink the well water.[6]

Step 2: Read the two lines on your result

Total coliform is a warning sign. If the count is high, other germs that can hurt you are likely in the water too.[2][3] E. coli is worse. It likely means poop got into your well.[7] Germs in water can give you a sick stomach.[8] Not sure the result is right? You can send a second sample to check it.[9]

Step 3: Call your local health department

They can help you read the result. They can tell you what to do next.[6]

Step 4: Look at the well

Walk out to the well. Is the cap loose? Does it have holes? Do you see cracks in the well?[10] Rain water should not run to the well.[11] Rain and melted snow can wash germs into a well. So can a leaking septic field.[12][13]

Step 5: Fix it, then treat the well

First fix what you found. Then treat the well. Then test again before you use the water.[14][15] After a flood, the CDC says a well or pump contractor should do this job.[16]

Step 6: Test again

If you used chlorine, wait at least 7 to 10 days. That lets the chlorine flush out. Then test.[17] Use a state-certified lab.[18]

Step 7: If the germs come back

Germs that come back can mean a bad seal around the well pipe.[11] Ask a well driller how to fix the seal.[19] If a treatment does not clear the germs, you may need to buy a system that kills germs in your water.[20]

Test your well

The CDC says to test at least once a year.[21] Use a state-certified lab.[18]

How to test your well

Straight answers

Can I drink well water with coliform in it?

Not yet. The CDC says do not drink well water if you think it has germs that can hurt you. Drink bottled water.[4] If you cannot, call your health department or a well pro before you drink it.[6]

What is the difference between total coliform and E. coli?

Total coliform is a warning sign that other germs may be in the water.[2] E. coli is worse. The CDC says it likely means poop got into the well.[7]

Is coliform common in well water?

It shows up a lot. In one study of 450 wells, about 1 in 3 had coliform.[5]

How long after a treatment should I test my well again?

The CDC says to wait at least 7 to 10 days after you use chlorine. That lets the chlorine flush out.[17] Use a state-certified lab.[18]

How often should I test my well?

The CDC says at least once a year. Test for total coliform, nitrates, total dissolved solids and pH.[21] Test again after a flood, after a well repair, or when the taste, color or smell changes.[22]

Who can help me read my test result?

Your local health department. The CDC says they can help you read the result and tell you what to do next.[6]

Read more

Sources

Each number on this page points here. We read each source on the date shown.

  1. [1] Penn State Extension: Coliform Bacteria“Most types of coliform bacteria are harmless to humans, but some can cause mild illnesses, and a few can lead to serious waterborne diseases.” Checked 2026-10-19.
  2. [2] Penn State Extension: Coliform Bacteria“Coliform bacteria are often referred to as 'indicator organisms' because they indicate the potential presence of disease-causing bacteria in water.” Checked 2026-10-19.
  3. [3] CDC: Guidelines for Testing Well Water“If the total coliform count is high in your water, it is likely that harmful germs ... are also in your water.” Checked 2026-10-19.
  4. [4] CDC: Guidelines for Treating Well Water“If your well is contaminated with harmful germs or chemicals, or you suspect it is, do not drink your well water. Instead, drink and use bottled water or water from another safe source.” Checked 2026-10-19.
  5. [5] Penn State Extension: Coliform Bacteria“A 2006 survey of 450 private wells found coliform bacteria in approximately 35 percent and E. coli bacteria in about 15 percent of private wells.” Checked 2026-10-19.
  6. [6] CDC: Guidelines for Testing Well Water“Contact your local health or environmental department. They can help you understand the test results and what to do next ...” Checked 2026-10-19.
  7. [7] CDC: Guidelines for Testing Well Water“A positive test for fecal coliforms or E. coli likely means that poop (feces), and the harmful germs in poop, have gotten into your well water.” Checked 2026-10-19.
  8. [8] EPA: Potential Well Water Contaminants and Their Impacts“People that consume drinking water containing microorganisms can experience gastrointestinal illnesses and infections.” Checked 2026-10-19.
  9. [9] Penn State Extension: Coliform Bacteria“You may want to submit a second sample just to confirm the initial result.” Checked 2026-10-19.
  10. [10] Oregon State University Well Water Program: Coliform Bacteria“Is the cap loose? Are there any open holes in the cap? Are there cracks or holes that you can see in the well?” Checked 2026-10-19.
  11. [11] Oregon State University Well Water Program: Coliform Bacteria“Make sure that runoff water does not reach the well. The presence of bacteria also means that there may be problems with the grout seal around the well pipe.” Checked 2026-10-19.
  12. [12] EPA: Potential Well Water Contaminants and Their Impacts“Water run-off from rainfall or snow-melt can contaminate private wells by washing microorganisms into the well system or seeping underground.” Checked 2026-10-19.
  13. [13] EPA: Potential Well Water Contaminants and Their Impacts“Leakage of waste from underground storage tanks and effluent from septic leach fields can reach a water source and result in microorganisms being present in water wells.” Checked 2026-10-19.
  14. [14] Oregon State University Well Water Program: Coliform Bacteria“FIX the problem, the shock chlorinate the well, and test again before you use the water.” Checked 2026-10-19.
  15. [15] CDC: Guidelines for Treating Well Water“Then, test the water to make sure the treatment worked before drinking or using it.” Checked 2026-10-19.
  16. [16] CDC: How to Disinfect Wells After an Emergency“Wells should be disinfected by a well or pump contractor, due to safety concerns.” Checked 2026-10-19.
  17. [17] CDC: How to Disinfect Wells After an Emergency“Wait at least 7 to 10 days to test the water after disinfection to ensure that the chlorine has been thoroughly flushed” Checked 2026-10-19.
  18. [18] CDC: Guidelines for Testing Well Water“Use a state-certified laboratory to test your water.” Checked 2026-10-19.
  19. [19] Oregon State University Well Water Program: Coliform Bacteria“contact a well driller to advise you on repairing the grout seal” Checked 2026-10-19.
  20. [20] Penn State Extension: Coliform Bacteria“If shock chlorination is unsuccessful at eliminating coliform bacteria from your water supply, you'll need to consider buying a disinfection treatment system.” Checked 2026-10-19.
  21. [21] CDC: Guidelines for Testing Well Water“Test your well water at least once every year for total coliform bacteria, nitrates, total dissolved solids, and pH level.” Checked 2026-10-19.
  22. [22] CDC: Guidelines for Testing Well Water“You should also have your well water tested if: You are notified that there are problems with well water in your area, There are problems near your well, such as flooding, land disturbances, or nearby waste disposal sites, You replace or repair any part of your well system, You notice a change in your water's taste, color, or smell, You or someone you live with becomes pregnant, A child starts living with you” Checked 2026-10-19.

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