Around the world, there is more salty groundwater than fresh, drinkable groundwater. For example, 60 percent of India is underlain by salty water -- and much of that area is not served by an electric grid that could run conventional reverse-osmosis desalination plants. Now an analysis by MIT researchers shows that a different desalination technology called electrodialysis, powered by solar panels, could provide enough clean, palatable drinking water to supply the needs of a typical village. The study, by MIT graduate student Natasha Wright and Amos Winter, the Robert N. Noyce Career Development Assistant Professor of Mechanical Engineering, appears in the journal Desalination.

Winter explains that finding optimal solutions to problems such as saline groundwater involves "detective work to understand the full set of constraints imposed by the market." After weeks of field research in India, and reviews of various established technologies, he says, "when we put all these pieces of the puzzle together, it pointed very strongly to electrodialysis" -- which is not what is commonly used in developing nations.

The factors that point to the choice of electrodialysis in India include both relatively low levels of salinity -- ranging from 500 to 3,000 milligrams per liter, compared with seawater at about 35,000 mg/L -- as well as the region's lack of electrical power. (For on-grid locations, the team found, reverse-osmosis plants can be economically viable.)

Such moderately salty water is not directly toxic, but it can have long-term effects on health, and its unpleasant taste can cause people to turn to other, dirtier water sources. "It's a big issue in the water-supply community," Winter says.