Microbial regrowth in drinking water distribution or premise plumbing systems can cause problems like growth of opportunistic pathogens (e.g. Legionella pneumophila), esthetic complaints or regrowth parameters exceeding legislative guidelines. The microorganisms responsible for these problems mainly multiply in biofilms on the pipe wall and/or sediment and will alter the water quality once they are released in the water. This release of biofilm organisms in the water phase is largely unexplored and will be the focus of this PhD project. The influence of pipe material, hydraulics and water quality on the release of biofilm organisms will be studied using cultivation-based and ‘state of the art’ molecular microbiological methods.