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One of the most common questions after receiving a microbiological water report is:
What is the difference between Total Coliforms and Escherichia coli (E. coli)?
Although these organisms are often reported together, they serve different purposes and provide different information about water quality.
Understanding the difference helps municipalities, food manufacturers, industrial facilities, environmental consultants, and water system operators make better decisions about water quality, treatment performance, and risk management.
Total Coliforms are a group of bacteria commonly found in:
Not all Total Coliforms originate from fecal contamination.
Because they are widely distributed in the environment, Total Coliforms are commonly used as indicators of general water quality and system integrity.
Escherichia coli (E. coli) is a specific member of the coliform group.
Unlike many Total Coliform bacteria, E. coli is strongly associated with the intestinal tract of humans and warm-blooded animals.
Because of this association, E. coli is commonly used as an indicator of potential fecal contamination.
Testing both organisms provides a more complete picture of water quality.
Is the water system showing signs of microbiological changes?
Is there evidence suggesting possible fecal contamination?
Together, these results help operators determine whether further investigation may be required.
Results are commonly reported as:
<1 CFU/100 mL | 2 CFU/100 mL | 10 CFU/100 mL
<1 MPN/100 mL | 2.2 MPN/100 mL | 9.8 MPN/100 mL
Not Detected | Detected
Total Coliforms: Not Detected | E. coli: Not Detected
Generally indicates good microbiological water quality at the time of sampling.
Decision Supported: Continue routine monitoring.
Total Coliforms: Detected | E. coli: Not Detected
May indicate: Environmental influences | Distribution system concerns | Biofilm development | Sampling location issues
Decision Supported: Review system conditions and consider follow-up monitoring.
Total Coliforms: Detected | E. coli: Detected
May indicate: Possible fecal contamination | Treatment concerns | Distribution system issues | Source water impacts
Decision Supported: Further investigation and corrective actions may be necessary.
Total Coliforms: Elevated Counts | E. coli: No E. coli Detected
May indicate changing system conditions without evidence of fecal contamination.
Decision Supported: Evaluate operational conditions and historical trends.
False. E. coli is one specific member of the larger Total Coliform group.
False. Many Total Coliform bacteria originate from environmental sources.
False. Other microbiological concerns may still exist and should be evaluated.
Total Coliform and Escherichia coli testing help organizations:
Understanding the difference between these indicators helps determine what actions, if any, should be considered next.
Not necessarily. Many Total Coliform bacteria occur naturally in the environment.
Yes. E. coli is a member of the coliform group.
They provide different information about water quality and contamination risks.
It may indicate environmental influences, system issues, or changing water quality conditions.
It may indicate possible fecal contamination and should be evaluated further.
E. coli generally receives greater attention because of its association with fecal contamination.
PBR Laboratories provides Total Coliform testing, Escherichia coli (E. coli) testing, microbiological water testing, potable water testing, environmental water monitoring, and wastewater testing throughout Alberta, Western Canada, and Canada.
Contact PBR to discuss water quality results, follow-up testing requirements, sampling programs, and compliance objectives.
Choose PBR – Because Precision Matters, Defining Excellence in Laboratory Services Since 1984.