Solar power turns saltwater drinkable

There's more than enough freshwater on Earth for humans to survive - but the problem is that it isn't very well-distributed. Northerly and equatorial countries have loads of it, but those in between are growing increasingly parched.

To address this issue, the United States Agency for International Development launched a competition to create an affordable desalination system. Entrants were judged on three criteria - their designs had to be cost-effective, energy-efficient and environmentally sustainable.

The winners of this competition have now been announced, with a team from MIT taking home the $140,000 first prize. They created a system that uses solar panels to charge batteries, which then are used to draw dissolved salt particles (which have a slight electric charge) out of the water. As well as pulling out the salt, the team exposed the water to ultraviolet light - which destroys bacteria and makes it safer to drink.

Most desalination plants use a technique called reverse osmosis to remove salt - using high pressure pumps. But this is an inefficient method, wasting 40 percent of the water. With MIT's method, just 5 percent of water is lost.

The team has built their technique into a single robust unit that can supply enough water every day to either irrigate a small farm or satisfy the drinking and cooking needs of up to 5,000 people. It's powered exclusively by the sun.

While the unit has been tested extensively in the United States, it hasn't yet been proved in the areas where it's need the most. A pilot project, involving rural farmers in the areas where the US Agency for International Development operates, will be the next step.