Water stored in dams and reservoirs for humans to use often evaporates, especially in hot regions like southern Africa. Rising temperatures speed up evaporation, leaving less water for people, farming and industry. Daniel Kwasi Kpeglo has just completed a Ph.D. in physics. He explains his laboratory research into a new design—a thin nanomaterial floating cover that could be placed over lakes and dams like a blanket, reducing evaporation by limiting the amount of infrared heat from the sun that reaches the water. He also outlines what hurdles need to be cleared for the design to be tested in the real world.