Minns Rd Tank B, 24 June 2016 (Melton)

“Issue – Routine sampling at the tank resulted in a detection of 1org/100ml of E.coli in the presence of 0.09mg/L total chlorine. Actions – The tank was offline at the time, and not supplying water into the reticulation network. The tank was kept offline for the entire week.

Resampling was conducted for three consecutive days with all results clear of E.coli. The reported routine result was declared as a false positive. The tank was inspected and laboratory and/or sampler error was suspected as the root cause. When the tank was brought back online, spot-dosing and additional sampling of the water was performed prior to connection to the reticulation network. Outcome – During early 2016, the tank was assessed by external consultants for refurbishment and to have a booster chlorinator installed in 2016/17.” Western Water

Escherichia coli should not be detected in any 100 mL sample of drinking water. If detected
in drinking water, immediate action should be taken including investigation of potential
sources of faecal contamination.

“Coliforms are Gram-negative, non-spore-forming, rod-shaped bacteria that are capable of aerobic and facultative anaerobic growth in the presence of bile salts or other surface active agents with similar growth-inhibiting properties. They are found in large numbers in the faeces of humans and other warm-blooded animals, but many species also occur in the environment.

Thermotolerant coliforms are a sub-group of coliforms that are able to grow at 44.5 ± 0.2°C. E. coli is the most common thermotolerant coliform present in faeces and is regarded as the most specific indicator of recent faecal contamination because generally it is not capable of growth in the environment. In contrast, some other thermotolerant coliforms (including strains of Klebsiella, Citrobacter and Enterobacter) are able to grow in the environment and their presence is not necessarily related to faecal contamination. While tests for thermotolerant coliforms can be simpler than for E. coli, E. coli is considered a superior indicator for detecting faecal contamination…” ADWG 2011