The twelfth event was a detection of E. coli from a routine sample taken on 10 February 2010 at Raleigh Street, Oakleigh, (one E. coli organism per 100 mL) with a free chlorine residual of 0.42 mg/L. The location of this sample point is located within the Brighton / Heatherton locality, which is supplied from Cardinia and Silvan Reservoirs via Notting Hill Tank. Melbourne Water inspected Notting Hill tank and a sample was taken the day before from the tank outlet, with

E. coli and a free chlorine residual out of the tank of 0.67 mg/L. The system was flushed, after which all system checks were clear and the resamples taken at the tap and two other nearby taps were clear of E. coli.

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

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