Worldwide, billions of people rely on water sources whose hygienic quality is unclear or difficult to monitor. Conventional microbiological analysis methods take up to 24 hours, are costly, and require specialized laboratories for evaluation. These delays complicate the provision of safe drinking water, decision-making during flood events, or in regions with insufficient laboratory infrastructure. Researchers at the Federal Institute for Materials Research and Testing (BAM) have now developed a portable rapid test capable of detecting the molecule urobilin at extremely low concentrations. Their study is published in ACS Sensors.