Interpreting the Results of Water Well Testing


The microbiological quality of your water is determined by looking for the presence of bacteria indicative of faecal (sewage) contamination — namely, total coliforms and Escherichia coli. Total coliforms occur naturally in soil and in the gut of humans and animals. Thus, their presence in water may indicate faecal contamination. E. coli are present only in the gut of humans and animals. Their presence therefore indicates definite faecal (sewage) pollution.

Total Coliforms

The presence of total coliform bacteria in well water is a result of surface water infiltration or seepage from a septic system. According to Health Canada’s Guidelines for Canadian Drinking Water Quality (Sixth Edition, 1996), drinking water should not contain more than 10 total coliform bacteria per 100 mL of water. Any water containing more than this amount should be resampled. If the repeat sample contains more than 10 total coliform bacteria per 100 mL, corrective action should be taken immediately.

Water containing fewer than 10 total coliform bacteria per 100 mL is considered marginally safe to drink. Nevertheless, the water should be resampled. If fewer than 10 total coliform bacteria per 100 mL are detected, the cause of contamination should be determined if possible and corrective action taken as appropriate.

E. coli

E. coli appear in water samples recently contaminated by faecal matter; thus, they indicate the possible presence of disease-causing bacteria, viruses or protozoa. Water containing E. coli is not safe to drink. Corrective action should be taken immediately.

The maximum acceptable concentration of E. coli is “0” per 100 mL of water.

Well Maintenance - Testing Well Water for Microbiological Contamination

Corrective Action for Water that Does Not Meet the Recommended Guidelines

Water Treatment Devices for Home Use

Back to Main Page - Coliform Bacteria

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