Drinking water flowing through flexible plastic tubes (PVC) causes the development of a thin film-like coating within 24 h. At this stage microorganisms could either not or rarely be seen. After 48 h the number of microorganisms has become greater. With increasing time of experiment the microbial community becomes more dense until after 72 h it covers the whole surface. Now the microorganisms are embedded in extracellular polymeric substances. The primary film seems to be important for the development of microorganisms in equipment and apparatus.