How to Test Your Well Water for Bacteria
Bacteria testing checks your well for coliform and E. coli, the core indicators of microbial safety. Here is how it works and what results mean.
Quick Answer
Have your private well tested for total coliform and E. coli at least once a year by a state-certified laboratory. Coliform and E. coli should both be absent. These bacteria cannot be seen, tasted, or smelled, so testing is the only way to know your water is microbiologically safe.
Why bacteria testing matters
Private wells are generally not regulated under the federal Safe Drinking Water Act, so no agency tests your water for you. As the well owner, routine bacteria testing is your responsibility. The EPA standards for public systems are useful reference points: total coliform and E. coli should be absent from a drinking water sample.
Total coliform bacteria are common in soil and surface water. Finding them in your well does not always mean sewage contamination, but it signals a pathway for contaminants to reach your water. E. coli specifically points to recent fecal contamination and a real risk of disease-causing organisms.
How to get a bacteria test
- 1Contact your county or state health department or a state-certified laboratory and request a sterile sample bottle and instructions.
- 2Collect the sample exactly as directed, usually from an indoor cold-water tap with the aerator removed, following the lab’s disinfection and timing steps.
- 3Keep the sample cold and deliver it within the lab’s holding-time window, often 24 to 30 hours.
- 4Review the certified report, which reports coliform and E. coli as present or absent.
A positive E. coli result is an emergency
| Indicator | What it suggests | Target result |
|---|---|---|
| Total coliform | A pathway for contamination exists | Absent |
| E. coli | Recent fecal contamination, higher pathogen risk | Absent |
Frequently asked questions
- Can I tell if my water has bacteria by how it looks or tastes?
- No. Harmful bacteria do not change the color, taste, or smell of water. Only a laboratory test can confirm whether coliform or E. coli are present.
- How often should I test for bacteria?
- At least once a year, and again after flooding, well repairs, or any change in taste, color, or clarity. Use a state-certified laboratory for health-based results.
Sources & references
- Well Testing — CDC, accessed October 29, 2026
- National Primary Drinking Water Regulations — US EPA, accessed October 29, 2026
This guide is documentary research and general information, not a laboratory analysis or professional assessment of your specific well. See our disclaimer.