The cost of desalination

September 17th, 2007
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“Water, water everywhere – but not a drop to drink” said English poet Samuel Taylor Coleridge of the sea in the “Rime of the Ancient Mariner”. That’s his spelling, not mine :).

With potable water being in short supply in many places, particularly in countries such as Australia; it seems logical to just distill/filter it from sea water doesn’t it? After all, there’s a lot of it. We could all then get back to hosing our driveways, leaving the tap running while we brush our teeth and watering our lawns for two hours a night over summer.

Not quite.

While it is an option, it’s turning out to be an incredibly expensive and complex approach; complete with wide ranginging negative environmental ramifications.

For example, I was reading today how the government of New South Wales (an Australian state) will pay the operators of Sydney’s desalination plant more than $1 million a week for 20 years even if the plant is not used to produce water. The $1.8 billion desalination plant is due to be built by 2009. This money will be found in part by a 33% increase in water charges over the next four years. The government views it is an insurance policy. Side note: it really drives home how bleak our water outlook is when an “insurance policy” of this size is being taken out for just one city.

This is the price Sydney-siders must pay for the mismanagement of water over generations and it’s a scenario that will be repeated many times over around the world. But we still haven’t learned. Many billions of gallons of water cascades off houses and building each year, into stormwater systems and then out into.. the sea. We’re effectively throwing something out, only to buy it back again, along with some nasty companion products.

Aside from the financial cost of desalination, it’s a very energy intensive process. According to this article on LiveScience, current desalination methods consume around 14 kilowatt hours of energy to crank out 1,000 gallons of desalinated water. The typical Australian uses somewhere in the region of 100 gallons a day (about 400 – 500 litres). USA consumption rate is pretty much the same. It’s pretty disgusting when you consider a human’s basic need for survival is around half a gallon or 2.5 liters a day.

As for environmental issues:

- Carbon dioxide and other emissions from the energy required to process the water

- Land area occupied by the desalination plant – these plants take up a huge amount of space

- Marine organisms being sucked up by water intakes

- The effluent in the waste is a heavily concentrated saline solution which has the potential to kill marine organisms in the area it’s discharged.

- The discharge is usually warmer than the surrounding water; which can also negatively impact on the delicate balance of marine habitats

While desalination is certainly a preferable option to dehydration, we need to view it purely as an emergency measure, not a solution. The problem is with strategies such as this is that we can understandably feel that a crisis has been averted and we can return to wasting water per usual. Our oceans may contain a stack of the precious liquid, but the devil is in the detail.

Pick up some simple water saving tips

Michael Bloch
Green Living
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