By the Closer Look Inspectors team · Facts checked October 2026 against Iowa DNR, Iowa HHS, State Hygienic Laboratory and EPA sources · About our inspectors
A positive E. coli result indicates that a waste source, such as a septic tank or animal feedlot, has a pathway to your water system. In a 2006 to 2008 University of Iowa survey of rural wells for Iowa DNR, 11% of samples had E. coli.
All the water tests we offer
Bacteria
Shows whether surface water or waste is reaching the well.
- Surface contamination reaching the well
- Fecal contamination from septic, manure or wildlife
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 rock and soil10 µg/L (EPA)
- Lead service lines, solder and brass fixtures
- ManganeseNatural manganese; a concern for infants
- 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 taste
- 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 shown are EPA drinking water standards. Compare your lab results with these values.
Health standard: Iowa Department of Natural Resources (DNR): private wells have no mandated state or national water quality standards, so use EPA standards for public water supplies. State Hygienic Laboratory: total coliform with E. coli present is unsafe, with serious health concerns.
Where E. coli comes from in Iowa wells
E. coli is a type of total coliform bacteria that is present in sewage. The State Hygienic Laboratory (SHL) says E. coli in drinking water indicates a pathway from a waste source, such as an animal feedlot, septic tank or cesspool leakage, to the water system. Iowa's private well rules set minimum distances to sources of contamination. They call for at least 50 feet from the tank of a septic system and at least 100 feet from its absorption area. Animal enclosures such as confinement buildings or open feedlots must be at least 100 to 200 feet away, depending on whether the rules class the well as deep or shallow. In the University of Iowa survey for DNR, E. coli turned up in 24 of 82 wells shallower than 50 feet, but in 10 of 266 wells deeper than 100 feet. Bacteria were more common in northwest, south-central and southwest Iowa, where wells are generally shallow.
Health effects and who is most at risk
CDC says E. coli are usually harmless, but some specific types can make you seriously sick. CDC adds that an indicator test for E. coli does not show whether the dangerous types are present. Iowa DNR says disease-causing bacteria such as E. coli can cause gastrointestinal illness, vomiting, diarrhea and severe dehydration. It can be life-threatening for infants, children, the elderly and anyone with a compromised immune system. SHL says water with total coliform and E. coli present is unsafe, with serious health concerns. It also says such water may carry microorganisms such as Salmonella, enteric viruses or parasites. DNR says water that contains E. coli should never be used for any purpose where people might touch or swallow it.
Signs and when to test
You cannot tell by look, taste or smell whether well water is safe; Iowa DNR says only lab analysis can show it. SHL recommends testing every year for total coliform bacteria and E. coli, and again whenever the taste, odor or appearance of the water changes. It says shallow or older wells, wells near livestock confinement areas, septic systems or agricultural fields, and wells that were flooded may need additional testing. SHL also says not to drink from a flooded well, since flood water carries microorganisms that can cause disease. Iowa DNR lists a brand new well and any service on the well, pump or water system as times to test. For a new, reconstructed or rehabilitated well, Iowa's rules call for a coliform and nitrate sample 10 to 30 days after it goes into service. Iowa DNR says the well owner is responsible for testing. A home purchase is a sensible time for a baseline result.
If your result is positive: what to do next
Do not drink the water or brush teeth with it unless it has been disinfected. SHL says to disinfect water by boiling it for one minute, or use a known safe source such as bottled water or water from a public supply. Wash dishes with disinfected or known safe water, or run the sanitation cycle on a dishwasher. The best approach, SHL says, is to find how and where contaminants are entering the system and eliminate the entry pathway. Iowa DNR says a certified well contractor can help diagnose water issues and advise on repairs or well replacement. DNR also lists shock chlorination among the work of certified well drillers and pump installers. Under Iowa's well rules, if a sample from a new, reconstructed or rehabilitated well detects bacteria, the disinfection must be repeated.
Facts checked October 2026 against: shl.uiowa.edu, iowadnr.gov, iowadnr.gov, cdc.gov, iowadnr.gov, legis.iowa.gov.
Iowa private well testing timeline
| Test | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 | Year 6 |
|---|---|---|---|---|---|---|
| Coliform bacteria | ||||||
| Nitrate | ||||||
| Arsenic |
When to test your water
- Every yearColiform bacteria and nitrate, the basic safety checks for a private well.
- At least onceArsenic and manganese. Iowa DNR's testing list repeats arsenic every 3 years.
- Before a baby drinks the waterNitrate. Water above 10 mg/L as nitrogen should not be used for infant formula or juice.
- When you buy a homeA full baseline while you can still ask questions or negotiate.
- New well or well workWhen a well is new and after service on the well or pump.
- After a flood or power outageIf flood water was near or reached the well, or an outage dropped the water pressure.
- When taste, color or smell changesA change in the water is a reason to test.
- Near a fuel tankVOCs, plus DRO for diesel and fuel oil. Iowa DNR names gasoline among the VOCs some wells are susceptible to, and Iowa's well rules list 100 feet between a well and a liquid fuel storage tank other than propane.
- City water in an older homeLead. Iowa DNR says homes built before 1986 are more likely to have lead pipes, fixtures and solder.
Based on: Iowa DNR private wells, Iowa DNR testing frequency, Iowa DNR why test, Iowa DNR floods, State Hygienic Laboratory, 567 IAC 49.
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How far a well must be from common hazards in Iowa
- Property line4 ft
- Building sewer line10 ft
- LP gas tank15 ft
- Roadside ditch15 ft
- Stream, pond, lake or wetland25 ft
- Septic tank50 ft
- Septic absorption field100 ft
- Fuel oil or gasoline tank100 ft
- Fertilizer or chemical storage150 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
Buying a home with a well in Iowa: what happens at the sale
- Groundwater Hazard StatementIowa Code 558.69 requires a groundwater hazard statement filed with the declaration of value when a listed condition (including any known well and its status under 455B.190, or a private sewage disposal system) exists on the property, signed by a seller or agent, with a copy given to the buyer.
- Wells on the propertyIf known wells are on the property, the statement must give the approximate location of each and its status under Iowa Code 455B.190 (abandoned wells properly plugged); the owner is responsible for the accuracy of the information.
- Septic time-of-transfer inspectionIowa Code 455B.172(11) requires a private sewage disposal system serving a building to be inspected before any transfer of ownership, by a DNR-certified inspector, and the county recorder will not record the deed without the report or a binding acknowledgment.
- Failing systemsA system that is failing to treat wastewater must be renovated to current standards by the seller or, by agreement and within a reasonable time set by the county board of health or DNR, by the buyer (455B.172(11)(c)).
The paperwork tells you a well exists, not what is in it. Add water testing to your inspection. Get a free instant quote
Quick answers
What does it mean if E. coli is found in my Iowa well water?
The State Hygienic Laboratory says E. coli in drinking water indicates a pathway from a waste source, such as an animal feedlot, septic tank or cesspool leakage, to the water system. With total coliform also present, it rates the water unsafe, with serious health concerns. CDC says a positive E. coli test likely means that feces, and the harmful germs in feces, have gotten into the well water.
Is E. coli in well water dangerous?
It can be. CDC says E. coli are usually harmless, but some specific types can make you seriously sick, and an indicator test does not show which types are present. Iowa DNR says disease-causing bacteria such as E. coli can cause vomiting, diarrhea and severe dehydration, and can be life-threatening for infants, children, the elderly and people with a compromised immune system.
How do I get rid of E. coli in my well?
The State Hygienic Laboratory says the best approach is to find how and where contaminants are entering the system and eliminate the entry pathway. Iowa DNR says a certified well contractor can help diagnose the problem and advise on repairs or well replacement. In the meantime, SHL says to use a known safe source such as bottled water or water from a public water supply.
Should I test for E. coli when buying a house with a well in Iowa?
Iowa DNR says the well owner is responsible for water testing, and that lab analysis is the only way to know if a water supply is safe. A home purchase is a sensible time for that baseline. The State Hygienic Laboratory recommends testing every year for total coliform bacteria and E. coli, and CDC advises using a state-certified laboratory.
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