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Receiving an Escherichia coli (E. coli) result is only the first step.
The more important question is: What does the result actually mean?
Whether you are managing a municipal drinking water system, industrial facility, food processing operation, environmental monitoring program, or private water source, understanding E. coli results is critical for making informed decisions.
PBR Laboratories helps clients understand results, evaluate risks, and determine appropriate next steps—not simply receive data.
Escherichia coli (E. coli) is a bacterium commonly found in the intestinal tract of humans and warm-blooded animals.
While many strains are harmless, E. coli is widely used as an indicator organism because its presence may suggest recent fecal contamination.
For this reason, E. coli testing is routinely performed for:
Results are typically reported using one of three formats.
Colony Forming Units estimate the number of viable bacteria capable of growing under laboratory conditions.
Examples: <1 CFU/100 mL | 1 CFU/100 mL | 5 CFU/100 mL | 20 CFU/100 mL
CFU reporting is commonly used in microbiological water testing programs.
Most Probable Number is a statistical estimate of bacterial concentration.
Examples: <1 MPN/100 mL | 2.2 MPN/100 mL | 9.8 MPN/100 mL
MPN methods are commonly used for drinking water and environmental water monitoring.
Some monitoring programs only determine whether E. coli was detected.
Examples: Not Detected | Detected
This approach is commonly used for screening and compliance monitoring programs.
Results should never be interpreted without considering:
The same result may have different implications depending on where the sample was collected.
Examples: <1 CFU/100 mL | <1 MPN/100 mL | Not Detected
Generally indicates that E. coli was not detected in the analyzed sample.
Decision Supported: Verification of microbiological water quality at the time of sampling.
Examples: 1 CFU/100 mL | 2 CFU/100 mL | 1 MPN/100 mL
May indicate: Early contamination events | Environmental influences | Distribution system concerns | Sampling anomalies
Decision Supported: Review sampling conditions and determine whether follow-up testing is warranted.
Examples: 10 CFU/100 mL | 20 CFU/100 mL | 50 CFU/100 mL
May indicate: Fecal contamination | Treatment performance concerns | Distribution system issues | Source water impacts
Decision Supported: Investigation, corrective action, and follow-up monitoring.
A positive E. coli result may suggest that fecal contamination has occurred. Potential contamination sources include:
Lakes, rivers, reservoirs, and runoff events.
Leaks, pressure losses, maintenance activities, or cross-connections.
Surface infiltration, flooding, or nearby septic systems.
Treatment systems may not be operating as intended.
Wildlife, agricultural activities, or changing environmental conditions.
E. coli is one of the most important microbiological indicators used in drinking water programs.
Decisions Supported: Public health protection | Treatment verification | Compliance monitoring | Distribution system assessments
Results may indicate environmental influences affecting water quality.
Decisions Supported: Watershed management | Source water protection | Environmental monitoring
Detection may suggest infiltration or source water impacts.
Decisions Supported: Well assessments | Groundwater investigations | Risk management
E. coli monitoring may be used to evaluate treatment performance and environmental discharge programs.
Decisions Supported: Treatment optimization | Compliance programs | Environmental monitoring
Appropriate actions depend on the water source, intended use, and monitoring program. Common next steps include:
Confirm sample collection requirements were followed.
Verify results and assess trends.
Review treatment performance and operational conditions.
Identify contamination pathways.
Compare current results to previous monitoring data.
Determine whether regulatory actions or notifications are required.
Interpretation depends on water type, intended use, and monitoring objectives.
Water quality decisions should consider historical trends and supporting information.
Many strains are harmless. Testing focuses on E. coli because it serves as an indicator of possible fecal contamination.
Provides additional information about microbiological water quality.
Evaluates general bacterial populations.
Provides operational and environmental context.
Helps identify environmental influences affecting water quality.
E. coli testing helps organizations:
The result itself is only part of the story.
Understanding what the result means is what supports effective decision-making.
E. coli was not detected in the analyzed sample above the reporting limit.
A low level of E. coli was detected and may warrant review depending on the water source and monitoring objectives.
It may indicate fecal contamination and should be evaluated within the context of the water system and monitoring program.
CFU measures colonies grown on media, while MPN provides a statistical estimate of bacterial concentration.
Because it is an indicator of potential fecal contamination and possible public health concerns.
Review sampling procedures, conduct follow-up testing, investigate potential contamination sources, and evaluate treatment performance.
PBR Laboratories provides microbiological water testing, E. coli testing, total coliform testing, potable water testing, environmental water testing, and wastewater monitoring services throughout Alberta, Western Canada, and Canada.
Contact PBR to discuss results, follow-up testing requirements, sampling considerations, and water quality monitoring programs.
Choose PBR – Because Precision Matters, Defining Excellence in Laboratory Services Since 1984.