This is the first of two articles looking at the increasing reliance of Australian cities on desalination to supply drinking water, with less emphasis on alternatives such as recycling and demand management. So what is the best way forward to achieve urban water security?
Removing salts and other impurities from water is really difficult. For thousands of years people, including Aristotle, tried to make fresh water from sea water. In the 21st century, advances in desalination technology mean water authorities in Australia and worldwide can supply bountiful fresh water at the flick of a switch.
Achieving water security using desalination is now a priority for the majority of Australia’s capital cities, all but one of which are on the coast. Using the abundance of sea water as a source, this approach seeks to “climate proof” our cities’ water supplies.
From the late 1990s to 2009 southeastern Australia suffered through the Millennium Drought. This was a time of widespread water stress. It changed the Australian water industry for ever.
All major water authorities saw their water storages plummet. Melbourne storages fell to as low as 25% in 2009. The Gosford-Wyong water storage, supplying a fast-growing area of more than 300,000 people on the New South Wales Central Coast, dropped to 10% capacity in 2007.
Modern industrial-scale desalination uses reverse osmosis to remove salt and other impurities from sea water. Water is forced under high pressure through a series of membranes through which salt and other impurities cannot pass.
Design, construction and maintenance costs of these industrial plants are high. They also use massive amounts of electricity, which increases greenhouse gas emissions unless renewable energy sources are used.
Just as many of the massive new desalination factories were completed, and proudly opened by smiling politicians, it started raining. The desalination plants were switched off as storages filled. However, water consumers still had to pay for the dormant plants to be maintained – hundreds of millions of dollars a year in the case of the Melbourne and Sydney plants.
Perth, Adelaide, Melbourne, Brisbane and the Gold Coast already have the capacity to supply larger proportions of their populations with desalinised water as required.
What about inland and regional settlements across Australia? Large-scale desalination plants may not viable for Canberra and other inland centres. These regions would require sufficient groundwater resources and extraction may not be environmentally sound.
In fact, water costs in general vary enormously, depending on location and how much is used. The pricing structures are about as complex as mobile phone plans or health insurance policies.
The highest price is in Canberra where residents pay $4.88/kL for each kL they use over 50kL per quarter. The cheapest rate is Hobart’s $1.06/kL.
The issue of water pricing leads on to the question of what happened to the alternative strategies – recycling and demand management – that cities pursued before desalination became the favoured approach? And how do these compare to the expensive, energy-hungry process of desalination? We will consider these questions in our second article.
This article has been updated to clarify the status of advice on Melbourne’s use of desalinated water.