These devices absorb heat from sunlight and use it to evaporate water, leaving behind contaminants and reforming as a liquid in a separate container, and although they work, they can be relatively expensive and inefficient. Researchers have now developed a new type of solar still using carbon-coated paper that they say is cheaper and more than twice as efficient as existing devices.

Solar stills can be live-saving devices for people in developing countries or disaster-affected areas, but there's room for improvement according to the team made up of members from the University at Buffalo (UB), China's Fudan University and the University of Wisconsin-Madison.

"People lacking adequate drinking water have employed solar stills for years, however, these devices are inefficient," says Haomin Song, a co-author of the study. "For example, many devices lose valuable heat energy due to heating the bulk liquid during the evaporation process. Meanwhile, systems that require optical concentrators, such as mirrors and lenses, to concentrate the sunlight are costly."