2009/10 + 2014/16: Fish Creek (Victoria) – Trihalomethanes, Chlorine

Fish Creek (Victoria) – Trihalomethanes

Highest Levels Only

2009/10 Fish Creek Trihalomethanes 0.250mg/L

2014/15 Fish Creek Trihalomethanes 0.280mg/L

Trihalomethanes Australian Guideline Level 250μg/L (0.25mg/L)

Why and how are THMs formed?
“When chlorine is added to water with organic material, such as algae, river weeds, and decaying leaves, THMs are formed. Residual chlorine molecules react with this harmless organic material to form a group of chlorinated chemical compounds, THMs. They are tasteless and odourless, but harmful and potentially toxic. The quantity of by-products formed is determined by several factors, such as the amount and type of organic material present in water, temperature, pH, chlorine dosage, contact time available for chlorine, and bromide concentration in the water. The organic matter in water mainly consists of a) humic substance, which is the organic portion of soil that remains after prolonged microbial decomposition formed by the decay of leaves, wood, and other vegetable matter; and b) fulvic acid, which is a water soluble substance of low molecular weight that is derived from humus”. Source: https://water.epa.gov/drink/contaminants/index.cfm

Fish Creek (Victoria) – Chlorine

…detection of free chlorine residual levels above the ADWG guideline value of 5 mg/L on Tuesday September 6th, 2016. During routine water quality sampling, a free chlorine residual of 8.0 mg/L was recorded at 9:30 am for the Fish Creek basin outlet post­secondary disinfection site. Chlorine mapping in the township of Fish Creek was immediately carried out to determine the spread and direction of travel of water with elevated chlorine residual in the reticulation system. Readings of between 0.7 to 8 mg/L were recorded at sites across town, including a tap at the Fish Creek primary school.


Based on health considerations, the guideline value for total chlorine in drinking water is 5 mg/L.

Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion. Chlorine and hypochlorites are toxic to microorganisms and are used extensively as disinfectants for drinking water supplies. Chlorine is also used to disinfect sewage and wastewater, swimming pool water, in-plant supplies, and industrial cooling water.

Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. Water authorities may need to exceed the odour threshold value of 0.6 mg/L in order to maintain an effective disinfectant residual.

In the food industry, chlorine and hypochlorites are used for general sanitation and for odour control. Large amounts of chlorine are used in the production of industrial and domestic disinfectants and bleaches, and it is used in the synthesis of a large range of chemical compounds.