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: