Leo Heijnen has worked on water quality at KWR since 2000. During this time he has built up a strong profile on health-related microbial water quality. Leo was a pioneer in the development and implementation of molecular, DNA-based, methods in the urban watercycle. Methods like qPCR and Next Generation Sequencing (NGS) have proven very valuable in rapidly and reliably detecting and identifying microorganisms in water. Molecular methods have evolved to become general-use research tools, enabling better insight into water quality and water treatment issues. In 2018 molecular methods have also become part of the routine monitoring of water quality. A validation study, performed in collaboration with the drinking water laboratories, resulted in legal acceptance of a molecular method for routine detection of E. coli in drinking water.