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Testing Your Well Water for Bacteria

Coliform bacteria are found in the environment and in the feces of humans and animals. Most coliform bacteria do not cause illness, but they can indicate that other disease-causing organisms are present in the water. Waterborne illness from these other organisms can cause nausea, vomiting, fever and diarrhea.

See our Water Testing Fees and Services page for additional water tests available!

How often should I test my well water for bacteria?

You should test your well every year for bacteria. In addition, test for bacteria if:

  • You notice a sudden change in your water's taste, appearance, or odor.
  • The water turns cloudy after rainfall or the top of the well was flooded.
  • You suspect a contamination source (sewage system, barnyard, etc.) is within 50 feet of your well.
  • Family members are experiencing unexplained flu-like symptoms.
  • Your water supply system has been serviced or you have made changes to the system.


How do I test my well water for bacteria?

Follow these sampling instructions carefully:

  1. Obtain sample bottles from the Environmental Health office.
  2. Wash your hands with warm water and soap before collecting the sample.
  3. Do not open the bottle until you are ready to collect the sample.
  4. Choose a clean, indoor faucet. Do not collect the sample from hose lines, from leaking/dirty faucets, or from reverse osmosis treated faucets.
  5. Turn on the COLD water and let it run at full stream for 5 minutes.
  6. Turn down the faucet to a small stream of the cold water.
  7. Open the bottle. Do not set the cap down. Do not touch the inside of the cap or bottle. Do not rinse out the bottle. Do not dump out any powder or pill that is inside the bottle, as this helps preserve the sample.
  8. Collect the water sample directly into the sample bottle. Fill to the neck of the bottle. Do not overflow. Do not allow the cap or bottle to touch the faucet.
  9. Replace the cap securely on the bottle.
  10. Place the bottle in a cooler with an ice pack during transport.
  11. Fill out the form completely. Attach the form to the bottle with a rubber band. Return the bottle to our office before 3:00pm, Monday - Friday.

 
What do my test results mean?

Coliform bacteria are found in the environment and in the feces of humans and animals. Most coliform bacteria do not cause illness. However, they can indicate that other disease-causing organisms may be present in the water. E. coli is a type of coliform bacteria that can cause very serious illness. It is found in the intestines of birds and mammals. If E. coli is found in a water supply, it can indicate that the water is contaminated with sewage. 

Annual water testing for coliform bacteria is advised. In addition, test if you notice a sudden change in your water’s taste, appearance or odor; the water turns cloudy after rainfall; the top of the well was flooded; you suspect a contamination source (septic system, barnyard, etc.) is within 50 feet of your well; or, family members are experiencing unexplained stomach flu-like symptoms.

Coliform Bacteria Absent: No coliform bacteria organisms were found in the water sample.

Coliform Bacteria Present: Coliform organisms were found in the water sample. This indicates possible pollution in your well. Do not drink or cook with this water. You need to disinfect your well and re-sample the water. Contact our office at 734-222-3800 for assistance. 

E. coli Level: If anything other than 0, Non-detect or ND is listed, it means that E. coli bacteria were found in the water sample. Do not drink or cook with this water. Well construction defects and routes for sewage contamination into the water supply need to be investigated. After any necessary repairs are made, you need to disinfect your well and re-sample the water. Contact our office at 734-222-3800 for assistance.   


What should I do if coliform bacteria are detected in my well?

Be concerned but do not panic if coliform bacteria are detected. Resample immediately if you have a positive sample before you treat, repair or replace the well. If you receive a second positive sample for total coliforms, or if the initial sample is positive for fecal coliforms, do not drink the water. Bring the water to a rolling boil for three minutes to kill the bacteria. You may also want to use bottled water as a temporary water source.


How can I eliminate coliform bacteria from my well water?

If coliform bacteria are present, the source of the problem should be identified. Resampling from several locations within the water system may be helpful. The entire water system may need to be thoroughly flushed and disinfected before a negative bacteria sample can be obtained. A well drilling contractor or a Washtenaw County Sanitarian can help identify structural defects in the system. After the defects are corrected, the system should be disinfected and the water retested before drinking.

How can bacteria get into drinking water?

Coliform bacteria do not occur naturally in groundwater. However, coliform bacteria can live within slime formed by naturally occurring ground water microorganisms. The slime (or biofilm) clings to the well’s screen, casing, drop pipe, and pump. Disturbances during well construction, pumping or maintenance can cause the slime to dislodge, releasing the coliform bacteria into the water. The following can also lead to contamination:

  • Missing/defective well cap - seals around wires, pipes or where the cap meets the casing may be cracked
  • Cracks or holes in the well casing - allow water that has not been filtered through the soil to enter the well (common in wells made of concrete, clay tile, or brick)
  • Many older wells were not sealed with grout when constructed - allows contaminant to seep into well
  • Well flooding - common problem for wellheads below ground in frost pits that flood during wet weather
  • Close proximity of a well to septic tanks, drainfields, sewers, drains, privies, barnyards, animal feedlots, abandoned wells and surface water - contamination can enter the well
  • Cross-connections with wastewater plumbing - wastewater can mix with the well water


For more information, please contact:

  • Your Area Sanitarian (based on your Township)
  • Washtenaw County Environmental Health Division - (734) 222-3800
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