Water Test Results Centre
How to read a bacteria result.
What present/absent coliform and E. coli results mean, when to resample, and why UV is not a first step on cloudy water.
Unit
Usually presence/absence, or colony counts (CFU/100 mL) depending on the method.
Canadian reference
E. coli should be absent in drinking water. Total coliform detections need follow-up with public health and a resample — they are not a DIY ‘maybe fine’.
Possible sources
Surface influence, damaged well caps, flooding, sewage, animal waste, or sampling error.
What one result cannot conclude
- A clear, odourless glass of water can still contain bacteria.
- A negative bacteria test says nothing about metals, nitrate or PFAS.
- A lighted UV lamp is not proof of disinfection.
Sensible follow-up testing
- Use your public-health instructions for resampling after a detection.
- On private wells, add chemistry once the supply is bacteriologically addressed.
Source correction
Health Canada advises identifying and correcting the contamination source where possible — well construction, drainage, sewage — not only adding treatment.
Certification questions
NSF/ANSI 55 Class A UV is intended to disinfect water that is otherwise visually clear. Class B is supplemental. Pretreatment for iron, manganese and turbidity is usually required.
Treatment options
Fix the source, shock/chlorinate when advised, then consider UV only on clarified water. Retest after work.
Related guide: how to test well water