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Water droplet splash

Credit: Laszlo Ilyes

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So far desalinisation sounds like a good option. There must be downsides, though?

There are indeed. Desalination uses a lot of energy and is therefore quite expensive in monetary and environmental terms.

Exactly how much energy is used depends on the location of the plant and the method used. For example, with the membrane desalinisation method, the saltier the water the more energy is needed to convert it to freshwater, while the warmer the water, the less energy is needed (which means a plant in cooler Hobart would require more energy than one in sweltering Darwin).

In terms of pollution, not only does the high-energy use result in greenhouse gas emissions, but there is also a constant stream of concentrated salt waste product being produced that must be disposed of.

Because of these downsides, for many countries desalinisation is generally used minimally and as a strong last resort in times of water crisis.

Can we get around these disadvantages?

Energy usage can be minimised through 'cogeneration' - where an electricity plant and a desalination plant are run together. The waste heat and excess power from the electricity production can be used to power the desalination plant more cheaply and efficiently.

We can also look towards running desalinisation plants on renewable energy.

Dealing with waste salt can be tricky. We can't simply dump it back into the ocean, as it could damage marine ecosystems. However, reintroducing it into the ocean together with wastewater could reduce the salinity to acceptable levels.

Alternatively, we could create special 'brine ponds' to dispose of the salt, or even consider the manufacturing of edible salt.

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