Taking a leaf out of nature's book, researchers in China have demonstrated how a device that mimics plant photosynthesis and transpiration could be used to bring clean water to the billion or more people across the globe who do not have access to this basic human right. Peng Tao, Wen Shang and colleagues built a three-layer membrane using titanium dioxide nanoparticles, gold nanoparticles and a supporting layer of anodized aluminum oxide. The device cleans water in two ways. First, in a process akin to photosynthesis traps, the titania captures light energy and this breaks down toxic pollutants in the water. Secondly, the gold nanoparticles cause an evaporative type process that leaves behind non-volatile pollutants as a residue.