By the Closer Look Inspectors team · Facts checked October 8, 2026 against MDH, MPCA and EPA sources · About our inspectors
E. coli is a type of coliform bacteria that indicates fecal contamination, typically from sewers, septic systems, or animal waste. MDH lists Minnesota sources as farms, feedlots, rural septic systems, wildlife, and aging city sewers. It can cause diarrhea, vomiting, and cramps, and infants, older adults, and people with weakened immune systems are at higher risk.
All the water tests we offer
Bacteria
Shows whether surface water or waste is reaching the well.
- Surface contamination reaching the wellNone should be present (MDH)
- Fecal contamination from septic, manure or wildlifeNone should be present (MDH)
Health chemicals
No taste, color or smell. These are the long-term health checks.
- Fertilizer, septic and manure; highest risk to infants10 mg/L (EPA)
- Natural arsenic from Minnesota rock and soil10 µg/L (EPA)
- Lead service lines, solder and brass fixturesNo safe level (MDH)
- ManganeseNatural manganese; a concern for infants100 µg/L for infants (MDH guidance)
- FluorideNatural fluoride; dental health4.0 mg/L (EPA)
- UraniumNatural radionuclide in groundwater30 µg/L (EPA)
Petroleum & solvents
Fuel and chemical spills from old tanks or nearby sites.
Household quality
Staining, scale and taste, and choosing the right treatment.
- IronRusty staining and metallic taste0.3 mg/L, aesthetic (MDH)
- HardnessScale buildup; sizing a water softenerNo health standard
- pHCorrosive or scaling water6.5 to 8.5, aesthetic (EPA)
- SulfateTaste and odor; diarrhea risk for infants250 mg/L, aesthetic (EPA)
Limits from MDH, EPA and MPCA. Your lab report compares each result to these values.
Health standard: MDH: safe drinking water does not have E. coli or other pathogens in it. EPA regulates it within the total coliform standard for public systems (no separate numeric value).
Where E. coli in well water comes from
E. coli is part of the fecal coliform group of bacteria found in feces. CDC explains that a positive E. coli or fecal coliform result likely means that feces, and the harmful germs they can carry, have entered the well water. Common sources include failing septic systems, animal waste, and standing water near the well. In Minnesota, MDH points to the same kinds of pathways that let coliform bacteria in: damaged or cracked casings, loose or missing well caps, leaking dug-well walls, and wells located too close to sewers, septic systems, or feedlots.
Health effects and who is most at risk
CDC notes that most E. coli is harmless, but some types can cause serious illness. A standard E. coli test does not show whether a dangerous type is present, so a more specific test is needed if that is suspected. Germs in contaminated water generally cause stomach pain and diarrhea, and MDH lists vomiting, cramps, nausea, fever, and fatigue among possible symptoms of waterborne microorganisms. Infants, children, elderly people, and people with weakened immune systems are more likely to become seriously ill, so treat any positive result as a reason to act.
When to test for E. coli
MDH recommends a coliform bacteria test for private wells every year, and CDC notes E. coli can be tested for on its own. Ask the accredited laboratory which bacteria results are included. CDC recommends testing when a well has been repaired, when flooding or waste problems occur nearby, when the water's taste, color, or smell changes, when someone in the home becomes pregnant, and when a child moves in. For a home purchase, a bacteria test reports the condition of the well on the day of sampling. An accredited laboratory analyzes the sample.
If E. coli is detected: what to do
CDC advises considering bottled water or another safe source and contacting your local health department. MDH recommends disinfecting the well with a chlorine solution, using a licensed well contractor or the MDH well disinfection instructions, then retesting at an accredited lab before using the water. Because coliform can regrow, MDH suggests another test about two to four weeks later. If disinfection repeatedly fails, MDH says to work with a licensed well contractor, who can clean or repair the well or build a new one.
Facts checked October 2026 against: cdc.gov, Minnesota Department of Health, Minnesota Department of Health.
E. coli water testing in pictures
Minnesota private well testing timeline
| Test | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 | Year 6 |
|---|---|---|---|---|---|---|
| Coliform bacteria | ||||||
| Nitrate | ||||||
| Arsenic | ||||||
| Lead |
Test again any time after flooding, after work on the well, or when the water's taste, color or smell changes, and always when you buy a home with a well.
How far a well must be from common hazards in Minnesota
- Building (closest projection)3 ft
- Lake, river, stream or pond35 ft
- Septic tank50 ft
- Drainfield (soil dispersal area)50 ft (100 ft sensitive well)
- Animal feedlot or building (over 1 animal unit)50 ft
- Cesspool or seepage pit75 ft (150 ft sensitive well)
- Unroofed feedlot, 300+ animal units100 ft
- Unprotected petroleum tank, 1,100+ gallons150 ft
Septic, feedlot or fuel tank near the well? A coliform and nitrate test shows whether it is reaching the water. Get a free instant quote
How long a private well lasts in Minnesota
Wells built before 1974, when Minnesota's well code began, are listed by MDH as higher risk for bacteria, along with leaking dug wells, wells in old frost pits and wells with corroded casings.
Wells built before 1974 often have no record on file. Test the water before you close. Get a free instant quote
Quick answers
What does it mean if E. coli is found in my well water?
It likely means feces, and the harmful germs they can carry, have entered the well. CDC notes most E. coli is harmless, but some types can cause serious illness, and a standard test cannot tell which type is present. Use bottled or another safe water source and contact your local health department.
Is E. coli in well water dangerous?
It can be. CDC says most E. coli is harmless but some types cause serious illness, and a standard lab test does not identify the dangerous types. Because a positive result points to fecal contamination, treat the water as unsafe to drink until the well is disinfected and retested negative.
How do I get rid of E. coli in my well?
Disinfect the well with a chlorine solution, either through a licensed well contractor or by following the MDH well disinfection instructions. Then have an accredited lab retest the water before you drink it. MDH suggests testing again two to four weeks later, and a contractor can look for the entry point if it returns.
Should I test for E. coli when buying a house with a well?
A bacteria test is a standard way to check a private well, and CDC advises well owners to test for coliform bacteria and E. coli. Results reflect the day of sampling, and an accredited laboratory analyzes the sample. A positive result can be addressed through disinfection, retesting, and inspection of the well.
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