Credit:SOURCE: Melbourne Water System Strategy Demand for water in and around Melbourne could grow by about 75 per cent in the next 40 years, while flows into the state's catchments could decrease by more than 40 per cent, according to projections published this month by City West Water, Yarra Valley Water and South East Water. According to the three state-owned corporations' 50-year urban water strategies, Melbourne's water supply is secure for another 10 to 15 years, "even under high climate change and high population growth scenarios", largely because of the desalination plant. Beyond that date, supply becomes uncertain. Environment Victoria's acting chief executive, Nicholas Aberle​, said the $6 billion desalination plant had given Melbourne a 10-year buffer to get its water supply under control.

Cameron FitzGerald, general manager of strategy and planning, CityWest Water on top of a 20 megalitre recycled water storage tank. Credit:Joe Armao "The risk is that we don't take this warning seriously until it's too late," Mr Aberle said. "We need to use that 10 years really wisely and to get serious about harvesting stormwater and re-using water for all sorts of purposes." Evidence suggests, however, that many Melburnians have begun to forget the lessons learned during the severe millennium drought of 1997 to 2009. Average residential water consumption rose to 166 litres a person a day in 2015-16, the highest level seen since the drought ended, figures from Melbourne Water show. It dipped slightly to 162 litres a day in 2016-17. Melbourne Water spokesman Joseph Keller said Melburnians were "encouraged to limit their consumption to 155 litres per person per day", in line with the government's Target 155 campaign.

This year has been dry with below-average rainfall in five of the first six months. Melbourne's dams were 72 per cent full at the start of summer last year and are 62 per cent full now. The millennium drought depleted Melbourne's water storages to 25 per cent, the lowest seen since the 1970s, before the vast Thomson dam was commissioned. The water strategies predict that droughts like it may occur more frequently as the climate changes. The potential shortage by 2028 is one of three possible scenarios modelled by Melbourne's water corporations.

If population growth and climate change occur more incrementally, it's predicted demand for water will exceed supply by about 2043. If Victoria avoids the impacts of climate change, and water consumption does not rise significantly, the city's supply will be secure for at least another 50 years. The strategies, which are based on guidelines for climate change adaptation set by the Andrews government, effectively rule out building another dam in Victoria, because it would exact too great a toll on the environment. "The removal of water from rivers, and the construction of any associated infrastructure such as weirs or dams, can have significant environmental and social impacts," the strategies state. "For these reasons, it is difficult to justify further investment in infrastructure to harvest more water from rivers."

Coalition water spokesman Peter Walsh criticised the advice against ever building another dam, arguing it could limit the ability to store water during future wet periods. "If you look at climate scenarios in future projections, it's likely that there will be more extreme events, wet and dry," Mr Walsh said. "So we should be storing water for the dry times. You never say never." What is recommended is boosting the $6 billion desalination plant, already one of the world's largest, from 1500 billion litres a year to 2000 billion litres, even though this would bring an increase in household water bills. Water bills rose $12 last year because of the first order of 50 billion litres from the Wonthaggi plant. One way the water corporations have already begun to boost water security is by recycling sewage into non-drinking water.

At the Western Treatment Plant on Melbourne's south-western periphery, City West Water's West Wyndham recycled water project has begun to provide recycled water to new outer suburban housing estates. A 20-megalitre tank feeds water to about 5000 homes in and around Werribee, via purple pipes that signify it is not for drinking. The water is a "shandy" of 50 per cent recycled water and 50 per cent drinking water. A salt-reduction plant is being built so the tank can provide 100 per cent recycled water. It will eventually service about 40,000 properties in Wyndham, one of Australia's fastest-growing municipalities. The $205 million project will save Melbourne an estimated 250 million litres of water a year, City West Water said.

Loading "As our city experiences growth, we wanted to position ourselves as providing a modern, long-term and secure supply for our residents," the corporation's general manager of strategy and planning, Cameron FitzGerald, said. It's a significant amount of water but it is also a relative drop in the ocean; about 0.1 per cent of Melbourne's current annual demand of 272 billion litres a year.