Gertjan Medema is principal microbiologist. He is also part-time chair on Water & Health at Delft University of Technology and visiting Hannah professor at Michigan State University. His research focusses on understanding of the (barriers against) transmission of infectious diseases via water systems as scientific basis for the design of safe water systems. This encompasses: (1) development of methods for detection/typing/source tracking of pathogens and antimicrobial resistance in water and soil; (2) observational, experimental and modelling research in to the occurrence, fate and transport of pathogens and antimicrobial resistance in water systems (wastewater, surface water, groundwater, drinking water, urban water systems, water reuse systems, aerosols); (3) assessment of the removal of micro-organisms by water treatment processes; (4) integrating this knowledge in global/national water-pathogen models and into quantitative risk assessment/health impact assessment; (5) advise on design of safe water systems and safe water policies and guidelines. He is an internationally recognized expert and scientific coordinator of the WHO collaborating centre on Water Quality and Health, active in the WHO working group on microbiology; advisor of EU DG Environment on drinking water and water reuse guidelines, IWA fellow and member of the IWA Strategic Council and the specialist group on Health-Related Water Microbiology.