“For decades, desalination has been the only reason that many places, from the Caribbean to the Emirates, have been habitable. It was so energy intensive that in the 1960s, some proposed using nuclear power to do it. The world’s largest desalination plant, in Ras al-Khair, Saudi Arabia, produces much of its water through evaporation. In this process, water is forced across a plastic membrane with holes so tiny only water molecules fit through, leaving behind salt and other impurities. At depth, seawater naturally wants to cross a desalination membrane, so long as the fresh water on the other side of it is being pumped to the surface.