Although bacteria are an inevitable – and important – component of drinking water, the colonization of pipes by pathogenic organisms can lead to microbiological quality problems. However, according to an Eawag/HSLU project co-funded by the Commission for Technology and Innovation (CTI), various measures can be taken to minimise this risk. Prevention starts with the choice of pipe material: the scientists developed test methods which make it possible to quantify – simply and rapidly – both the release of organic carbon compounds from a material and microbial growth on pipe surfaces and in water. Pipes made of soft plastics and elastomers, in particular, show an undesirably high migration und biomass formation potential. When new plumbing systems are first filled, the use of microbiological filters and immediate flushing with mains water can further reduce the risk of contamination. Lastly, regular flushing of the system after commissioning and before (and after) the building is occupied can prevent prolonged stagnation and thus deterioration of water quality.