Temperature differences in the Arabian sea are used for desalination

Flickr/bunnicula

The people of the southwest Indian island of Karavatti are using the ocean's own thermal gradients to desalinate seawater and make bad drinking water a thing of the past, reports Yudhijit Bhattacharjee in this Science article.

Most desalination plants remove the salt from seawater either by boiling it and condensing the steam, or by pumping it across a salt-retaining membrane, but these methods are expensive.

The Karavatti plant, built by India's National Institute of Ocean Technology, uses a process akin to rain formation. Warm surface water is pumped into an onshore vacuum chamber, where some of the water vaporises.

Cold water drawn from 350 metres below the sea's surface then condenses the vapour in an adjoining chamber.

Using this process, called low-temperature thermal desalination, the plant produces 100,000 litres of fresh water a day. Although the process consumes 30 per cent more energy than its rival technologies, installing more chambers should make it more efficient and — at US$1 per 1,000 litres — cheaper.

Plans are afoot to build ten more plants on neighbouring islands. But on the mainland, where cold deep water is farther offshore, the method may be harder to implement.