March 2013: Routine sampling resulted in a Single E.coli detection at Williams Rise Tank. The tank had only been placed on the routine monitoring program in March 2013.

Response to Incident

“…it was found that the gantry was positioned directly above the lip of the access hatch.  There were bird droppings in a concentrated area of the roof, near the access hatch, indicating that birds were roosting on the gantry. With the amount of droppings on the roof, it was conceivable that with heavy rain the droppings could be washed into the tank. As a result, the gantry was moved away from the roof of the tank and the droppings were soaked in sodium hypochlorite and scrubbed off. The tank was spot dosed again and the reticulation system below the tank was flushed… (Western Water Water Quality Report 2012/13)

“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