It’s remarkable how simple the idea is: This paper sheet filters contaminated water to make it drinkable. The paper contains nanoparticles of silver or copper which kill bacteria in the water as it passes through, and is proving to be full of potential for communities in developing countries who don’t have access to clean water. In trials at 25 contaminated water sources in South Africa, Ghana and Bangladesh, the paper successfully removed more than 99% of bacteria. The safety level of the water after filtering it was equal to that of the North American tap water. According to the World Health Organization, 750 million people around the world lack access to safe water. A “drinkable book” full of these paper sheets could provide them with a cheap and easy solution for filtering water from nearby rivers and streams.