The water in Sydney Harbor–which is salty and polluted by sewage, toxic chemicals, and microplastics–isn’t drinkable. But researchers in Australia recently tested a new type of water filter that purified and desalinated the water in a single step. The same process could potentially be used to help the 2 billion-plus people around the world who lack access to safe drinking water. The filter uses Graphair, a type of graphene, a material made from a thin layer of pure carbon. A film made from the new version of the material, with microscopic nano-channels, has a “unique atomic structure where the channel...