Guidelines for Canadian drinking water quality : Guideline technical document - Escherichia coli

This guideline technical document reviews and assesses available literature on the uses of E. coli as an indicator of pathogen presence in source waters, the potential for E. coli to be present in the absence of recent faecal contamination, and improvements in methods for the detection of E. coli. [...] Monitoring for E. coli in treated water at the treatment plant and in the distribution system is carried out to provide information on the adequacy of drinking water treatment and on the microbial condition of the distribution system. [...] 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. [...] Only a history of data together with the verification of the suitability of the system design and its operation and maintenance can be used to confirm the long-term integrity of a supply.