The researchers from Empa and Eawag tackle these miniscule pathogens using two clever tricks: First, a temporary reduction in pH causes the tiny viruses, which are only about 70 nanometres across, to clump together and form larger aggregates. These then adhere to newly developed, positively charged ceramic-copper composites with a large surface area. Although the technology has not yet reached the stage where it can be put into practice, the researchers are confident that they have identified a cost-effective and sustainable approach that will pave the way for advances in water treatment in developing countries.