If we need power to turn the ocean into tap water, why not let the ocean provide the energy? Stephen Salter at Edinburgh University is working toward that possibility his Edinburgh Duck, a wave powered desalination plant. The device would work by using the force of the ocean to lower the pressure within the device, creating water vapor even at low temperatures. No electricity is generated or needed, no membranes need to be cleaned or replaced, the device simply sucks water vapor from the seawater, condenses it, and then uses the power of the waves to pump it back to shore via it's tube-like tethers.
Right now the device pumps only air, and not even very much air at that, but Salter says the concept could be expanded to create Ducks up to ten meters in diameter that would pump out 2000 cubic meters of water every day, enough fresh clean water for roughly 20,000 people (not including agriculture.)Detractors say that there is no way to scale up the Edinburgh Duck to the levels of performance seen in electric desalination plants. But we say that the Ducks can be decentralized and used locally only where they're most needed. Plus they don't pump out huge quantities of super concentrated salt water or require hundreds of megawatts per day to perform.
Pictured above is a scale model of the desalinization duck (left), and a 1976 image of a energy-producing duck design (right).