Sustainable biological filters called slow sand filters have been used to filter drinking water since the 1800s. They don’t use any chemicals, create no waste and use very little energy. However, technologies that meet modern requirements for control, monitoring and time-efficiency have become popular, while biological water treatment has been less favoured, since little has been understood about how it works. New research from Lund University in Sweden shows that not only are the older filters more efficient cleaners – they could be making a comeback soon with the help of new technology.