Douglas fir wood can be turned into a water filterJanet Horton / Alamy Stock Photo Slices of wood can act as water filters that remove bacteria and microplastics with more than 99 per cent efficiency, potentially offering a cheap way to protect people from water-borne illnesses. Previous research has investigated more complex methods to make wooden filters involving complex chemical treatments, but these would be impractical in lower-income countries where water-borne illnesses cause hundreds of thousands of deaths a year, say Antoni Sánchez-Ferrer and Jenifer Guerrero Parra at the Technical University of Munich, Germany.