https://southeastwater.com.au/SiteCollectionDocuments/AboutUs/WaterQualityReport201516.pdf
10 Feb 2023 The Basin Elevated Tank
A routine sample collected on 10 February 2023 returned an E. coli result of 2 orgs/100mL from a sample tap located at The Basin Elevated Tank outlet. Other samples collected on the same day from the upstream tank and the water supply network were all clear of E. coli.
Water supplied to The Basin Elevated Tank comes from Melbourne Water’s Silvan Reservoir. Silvan water supplies Melbourne Water’s Boronia Reservoir, which has secondary disinfection on the reservoir outlet. It’s then transferred to our The Basin No.2 Tank which then pumps water to The Basin Elevated Tank. This area has historically had low chlorine residuals.
Once notified of the results, re-samples were collected from The Basin Elevated Tank, as
well as upstream and in the elevated tank supply network.
The Basin Elevated Tank was then isolated from supplying the network, with the customers
being supplied from The Basin No. 2 Tank instead, which was spot dosed with chlorine to
improve residuals in the area. The water supply area was thoroughly flushed, with post-corrective action samples then collected from the same taps.
The following day the results were received, with one customer sample tap in the pre-flush
samples returning a positive result for E. coli of 2 orgs/100mL. All other samples were clear.
All post-flush samples were clear of E. coli. The Basin Elevated tank was then drained, cleaned, and inspected. No cause of
contamination was determined, however based on the resample results, it is believed to
have been a real contamination event.
After the tank had been cleaned and a reinstatement plan approved, including testing of the
tank, it was reinstated back into supply.
A secondary chlorination unit has been installed in this area, increasing the chlorine
residuals in the tank and the water supply network.
E.coli ADWG
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