Bacteria, Viruses, and Parasites in Drinking Water

Bacteria, Viruses, and Parasites in Drinking Water

Bacteria are everywhere in our environment, including Minnesota’s surface waters and groundwater. Some of these bacteria can be harmful to human health. Drinking water with disease-causing bacteria, viruses, or parasites (collectively called pathogens) can make you sick. It is not practical to test drinking water for every type of pathogen, but it is simple to test drinking water for coliform bacteria. The presence of coliform bacteria can indicate there may be harmful pathogens in the water.

This information is also available as a PDF document: Bacteria, Viruses, and Parasites in Drinking Water (PDF)

The presence of coliform bacteria, specifically E. coli (a type of coliform bacteria), in drinking water suggests the water may contain pathogens that can cause diarrhea, vomiting, cramps, nausea, headaches, fever, fatigue, and even death sometimes. Infants, children, elderly people, and people with weakened immune systems are more likely to get sick or even die from pathogens in drinking water.

The U. S. Environmental Protection Agency (EPA) requires public water systems to regularly test water for total coliform bacteria and E. coli. Safe drinking water does not have E. coli or other pathogens in it.

If you have a private well

Here are some recommendations on how to prevent and address coliform bacteria contamination:

Prevent Contamination

  • Protect Your Well by constructing it in a safe spot.
  • Regularly inspect your well for damage. Contact a Licensed Well Contractor if you find any damage.
  • Test your well water every year for coliform bacteria. You are responsible for keeping your well water safe and testing it as needed. All well testing should be done through an accredited laboratory. Contact a Minnesota Department of Health (MDH) accredited laboratory to get a sample container and instructions on how to submit a sample. You can also contact your county to see if they have any programs to make testing your water easier.
  • Disinfect your well with a chlorine solution if floodwaters come within 50 feet of your well; your water changes in taste, appearance, or odor; or your well is opened for servicing. Follow these steps for Well Disinfection or hire a Licensed Well Contractor.
  • Conduct routine maintenance of potential sources of contamination, such as household septic systems.

Address Contamination

If coliform bacteria are detected in your water, follow these steps:

  • Stop using the water for drinking and preparing food, unless you boil it at a full rolling boil for a full minute before using it. You can also use bottled water or water from a known safe alternative source.
  • Disinfect your well with a chlorine solution, using the same Well Disinfection steps as above.
  • Test your well water again after disinfection to confirm there are no coliform bacteria.
  • You can use the water again, without boiling, once the well has been disinfected and the water no longer tests positive for coliform bacteria. Contact MDH (800-383-9808 or with questions.

If you are on a public water system

Your public water system is regularly tested for coliform bacteria. The system will issue a public notice within 24 hours if it detects E. coli. The public notice will tell you what you should do to stay safe.

You can find the coliform bacteria test results for the system serving where you live by reading the system's Water Quality Report (also known as a Consumer Confidence Report [CCR]). You can call your public water system to get a paper copy of your CCR, or you may be able to find it online at Find Your Local CCR. You can find the coliform bacteria test results for the systems serving places other than where you live by contacting the water system.

Fecal matter contains many pathogens. Common sources of fecal matter in our environment include sewers, septic systems, and animal wastes. Pathogens from these sources can get into our drinking water. Testing drinking water for coliform bacteria is a simple way to find out if there may be pathogens in the water. If water also tests positive for E. coli bacteria, the water has fecal matter in it.

As an agricultural state, Minnesota has many farms and feedlots. Rural homeowners rely on septic systems to treat their household wastes. We have abundant wildlife, often in close proximity to people. Additionally, city sewer systems are aging and can leak. Fecal matter from any of these sources can get into lakes, streams, rivers, and sometimes groundwater. Minnesota’s public water systems and MDH regularly test for coliform bacteria in public water systems and work together to correct problems if water tests positive for coliform bacteria.

All newly constructed drinking water wells in Minnesota are tested for coliform bacteria. If coliform bacteria are detected, Minnesota’s Well Code requires the well contractor disinfect the well and confirm it is free of coliform bacteria before the well is put into use. Testing beyond this initial sample is the responsibility of the private well owner.

MDH regulates public water systems by:

  • Approving public water systems’ construction and treatment plans
  • Enforcing the Safe Drinking Water Act
  • Testing public water supplies

MDH regulates private and public wells and works with private well owners by:

MDH is also conducting a Pathogen Project to learn about the presence of viruses in Minnesota groundwater and what it means for public health.

Updated Friday, 22-Oct-2021 14:28:40 CDT