Guidelines for Canadian drinking water quality : Guideline technical document - total coliforms

Monitoring for total coliforms at the treatment plant and in the distribution and storage system is carried out to provide information on the adequacy of drinking water treatment and on the microbial condition of the distribution system. [...] In municipal-scale systems, the detection of more than 10% of samples in a given sampling period, or of consecutive samples from the same site, that are positive for total coliforms indicates changes in the quality of the water and a need for follow-up actions to be initiated. [...] In a distribution system, the number of samples for this bacteriological testing should be increased in accordance with the size of the population served, and the samples should be taken at regular intervals throughout the month. [...] While the required frequency for all testing at the treatment plant is prescribed by the responsible authority, best practice commonly involves a testing frequency beyond these minimum recommendations based upon the size of system, the number of consumers served, the history of the system, and other site-specific considerations. [...] Role of total coliforms in maintaining drinking water quality The best means of safeguarding against the presence of waterborne pathogens in drinking water is the application of the multi-barrier approach.