Operator terms · Water and wastewater
What are coliform bacteria?
Coliform bacteria are a group of bacteria used as an indicator of water safety. Most are harmless, but their presence signals that disease-causing organisms could get in too. Total coliform is a general screen; E. coli points more directly to fecal contamination. Operators sample for them to confirm the water is safe.
Last reviewed 2026-08-03
Why use an indicator
Testing for every possible pathogen is impractical. Coliforms are easy to detect and live wherever contamination can enter, so finding them warns that unsafe organisms might be present too.
Total coliform and E. coli
Total coliform is a broad screen for a possible pathway in. E. coli, a specific coliform, points more directly to fecal contamination and is a stronger warning.
Common questions
- Are coliforms themselves dangerous?
- Most are harmless; they are used as a warning indicator, not the main threat.
- What does a coliform-positive sample mean?
- A possible pathway for contamination, so the system investigates and re-samples.
- What is E. coli here?
- A coliform that points more directly to fecal contamination.