How clean is Melbourne's water?

Melburnians were recently hit with a ‘boil water’ notification after heavy winds caused extensive power outages, including one at the Silvan Dam water treatment plant in the city’s eastern outskirts.


A significant amount of untreated water entered Melbourne’s water mains as a result, forcing authorities to recommend households boil their tap water before consumption.


This left many asking - just how bad is Melbourne’s water, if left untreated?


When comparing major cities, Melbourne's tap water is actually the purest in Australia and sits alongside best in the world.


The chart below shows this by comparing two non-toxic contaminants (dissolved salts and hardness) in Australia’s major cities’ water supplies:

Average dissolved salts and hardness in Australia’s major cities’ water supplies


One might assume Melbourne’s water supply receives extensive treatment to achieve such results; however the opposite is true. Melbourne’s water is sourced from some of the most pristine catchments in the world and undergoes very little treatment.


Most of the water is drawn from large mountainous areas where human activity is not allowed, minimising the risk of contamination. Protected storage dams let the water sit for up to four years, allowing naturally occurring sediments to settle out via ‘organic’ filtration.


The water is so pure that authorities actually add elements when treating it. Three main treatments methods are used:

  1. Disinfection – this ensures there are no unwanted microbiological contaminants living in the water. It is carried out by adding chemicals such as chlorine gas or sodium hypochlorite to the water. Ultraviolet (UV) radiation treatment is also used for some catchments.

  2. Fluoridation – the adjustment of the element Fluoride in a water supply. This aims to improve the dental health of Melburnians and is carried out by adding a small amount of fluorosilicic acid (FSA) to the water.

  3. Neutralisation – this involves neutralising the pH of the water using a small amount of lime or caustic (sodium hydroxide).

Compared to most cities around the world that are forced to adopt a range of expensive water treatment technologies in order to meet World Health Organisation drinking water standards, Melbourne’s water supply undergoes an incredibly small amount of treatment.

Melbourne’s Silvan water dam. Source: Wikimedia Commons


The advantage to having a natural low-cost, high-quality water supply may not be something Melburnians regularly think about – especially when on the receiving end of a ‘boil water’ notice! However, the fact that only this notice was required when the city’s Silvan water treatment plant went unexpectedly offline highlights how valuable this water supply is.


Such an event could spell disaster in other cities around the world.

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