{"id":7218,"date":"2020-03-03T14:57:50","date_gmt":"2020-03-03T09:57:50","guid":{"rendered":"http:\/\/www.cawater-info.net\/all_about_water\/en\/?p=7218"},"modified":"2020-03-03T14:58:21","modified_gmt":"2020-03-03T09:58:21","slug":"cities-turn-to-desalination-for-water-security-but-at-what-cost","status":"publish","type":"post","link":"http:\/\/www.cawater-info.net\/all_about_water\/en\/?p=7218","title":{"rendered":"Cities turn to desalination for water security, but at what cost?"},"content":{"rendered":"

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?<\/em><\/p>\n

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Removing salts and other impurities from water is really difficult. For thousands of years people, including\u00a0Aristotle, 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.<\/p>\n

Achieving water security\u00a0using desalination is now a priority for the majority of Australia\u2019s capital cities, all but one of which are on the coast. Using the abundance of sea water as a source, this approach seeks to \u201cclimate proof\u201d our cities\u2019 water supplies.<\/p>\n

It\u2019s hard to believe now that as recently as 2004 all Australian capital city water authorities relied on surface water storage dams or groundwater for drinking water supplies. Since Perth\u2019s first desalination plant was completed in 2006, Australian\u00a0capital cities have embraced massive seawater desalination \u201cwater factories\u201d\u00a0as a way to increase water security.<\/p>\n

Perth and Adelaide have\u00a0relied most on desalination\u00a0to date. Canberra, Hobart and Darwin are the only capitals without desalination.<\/p>\n

The drought that changed everything<\/h2>\n

From the late 1990s to 2009 southeastern Australia suffered through the\u00a0Millennium Drought. This was a time of widespread water stress. It changed the Australian water industry for ever.<\/p>\n

All major water authorities saw their water storages plummet. Melbourne storages\u00a0fell 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,\u00a0dropped to 10% capacity\u00a0in 2007.<\/p>\n

These were familiar issues in locations such as Perth, where the big dry is epic. For more than four decades, the city\u2019s residents have been watching their\u00a0supply of surface water dwindle. Remarkably, only about\u00a010% of Perth\u2019s water now comes from this source.<\/p>\n

Perth\u2019s two desalination plants have a\u00a0combined output of up to 145 billion litres (gigalitres, GL) a year. That\u2019s nearly half the city\u2019s water needs.\u00a0Both have remained in operation\u00a0since they were built.<\/p>\n

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The Queensland Labor caucus applauded a protester advocating the alternatives in 2007, but by 2009 the Gold Coast desalination plant was ready to supply up to a quarter of southeast Queensland\u2019s needs. Dave Hunt\/AAP<\/p><\/div>\n

Modern industrial-scale desalination uses\u00a0reverse osmosis\u00a0to 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.<\/p>\n

Design, construction and maintenance costs of these industrial plants are high. They also\u00a0use massive amounts of electricity, which increases greenhouse gas emissions unless renewable energy sources are used.<\/p>\n

Another concern is the return of the excess salt to the environment. Australian\u00a0studies have shown minimal impact.<\/p>\n

Just as many of the massive new desalination factories were completed, and proudly opened by smiling politicians, it started raining. The\u00a0desalination plants were switched off as storages filled. However, water consumers still had to pay for the dormant plants to be maintained \u2013 hundreds of millions of dollars a year in the case of the\u00a0Melbourne\u00a0and\u00a0Sydney\u00a0plants.<\/p>\n

Bringing plants out of mothballs<\/h2>\n

Now drought has returned to southeast Australia. Once again,\u00a0many capital city water storages are in steep decline. So what is the response of water authorities in the desal age? Not surprisingly,\u00a0more desalination is their answer.<\/p>\n

One by one the desalination plants are being switched back on. Sydney has just\u00a0begun the process of restarting its plant, which was commissioned in 2010. Adelaide has plans to\u00a0greatly increase the modest output\u00a0from its plant this year. The Gold Coast plant, which can also supply Brisbane, is\u00a0operating at a low level in \u201chot standby\u201d mode.<\/p>\n

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The Adelaide desalination plant can produce up to 100 gigalitres a year \u2013 about half of Adelaide\u2019s annual water needs.\u00a0Sam Mooy\/AAP<\/p><\/div>\n

After a dry winter, Melbourne Water is expected to advise the Victorian government to make the largest orders for desalinated water since its plant, able to produce 150GL a year, was completed in December 2012. Mothballed for more than four years, it supplied its first water to reservoirs in March 2017. The previously forecast need for 100GL in 2019-20 (annual orders are decided in April) is almost one-quarter of Melbourne\u2019s annual demand. Plant capacity is capable of being expanded to 200GL a year.<\/p>\n

When bushfires recently threatened Victoria\u2019s largest water storage, the Thomson Dam, the government said desalinated water could be used to\u00a0replace the 150GL a year taken from the dam.<\/p>\n

Sydney\u2019s plan for future droughts is to\u00a0double the output of its desalination plant from 250 million litres (megalitres, ML) a day to 500ML a day. This would take its contribution from 15% to 30% of Sydney\u2019s water demand.<\/p>\n

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Being close to the sea is essential for a desalination plant the size of Sydney\u2019s, which can supply 91GL a year \u2013 around 15% of the city\u2019s needs \u2013 and is designed to double that in future. Sydney Water\/AAP<\/p><\/div>\n

Perth, Adelaide, Melbourne, Brisbane and the Gold Coast already have the capacity to supply larger proportions of their populations with desalinised water as required.<\/p>\n

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.<\/p>\n

How much, then, do we pay for the water we use?<\/h2>\n

The plants supplying our biggest cities\u00a0cost billions to construct and maintain, even when they sit idle for years.<\/p>\n

The Australian Water Association estimates the\u00a0cost of supplying desalinated water varies widely, from $1 to $4 per kL.<\/p>\n

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.<\/p>\n

The highest price is in Canberra where residents pay\u00a0$4.88\u00a0for each kL they use over 50kL per quarter. The cheapest rate is Hobart\u2019s\u00a0$1.06\/kL.<\/p>\n

The issue of water pricing leads on to the question of what happened to the alternative strategies \u2013 recycling and demand management \u2013 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.<\/p>\n

Source:\u00a0https:\/\/theconversation.com\/<\/a><\/p>\n

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