A drought? Seawater cheaper than tap water

Engineers at MIT have developed a solar-powered saltwater purifier so efficient that its production cost could be lower than that of conventional tap water.

In an article appearing in the journal Joule, the team describes the design of a new solar desalination system that takes saltwater and heats it with natural sunlight.

The device's configuration allows water to circulate in swirls, similar to the much larger "thermohaline" circulation of the ocean. This circulation, combined with solar heat, causes the water to evaporate, leaving behind salt. The resulting water vapor can be condensed and collected as pure drinking water. Meanwhile, the excess salt continues to circulate through and out of the device, rather than accumulating and clogging the system.

The new system has a higher water production rate and salt rejection rate than all other passive solar desalination concepts currently being tested.


Researchers estimate that if the system is scaled up to the size of a small suitcase, it could produce between 4 and 6 litres of drinking water per hour and last for several years before needing replacement parts. At this scale and performance, the system could produce drinking water at a cheaper rate and price than tap water.

"For the first time, it may be possible for water produced by solar light to be even cheaper than tap water," says Lenan Zhang, a research scientist at MIT's Device Research Laboratory.

The team envisions that a larger-scale device could passively produce enough drinking water to meet the daily needs of a small family. The system could also supply isolated coastal communities off the grid where seawater is readily accessible.