Small-scale heterogeneity in drinking water biofilms

The goal of this study was to characterize mature drinking water biofilms that grew inside flexible shower hoses. We aimed to identify environmental factors that shape biofilm heterogeneity and elucidate the importance of sample scale in both fundamental and applied biofilm research. Our hypothesis was that a biofilm grown on a single material under uniform conditions should be homogeneously distributed with respect to structure and composition. To test this, biofilms were grown inside identical flexible plastic hoses (PVC-P) under defined and controlled laboratory conditions and under real-use conditions. Small-scale heterogeneity was assessed by comparing (1) biofilm structure and thickness, (2) total cell concentrations, and (3) bacterial community composition of a total of 200 sections of 1.2 cm for each hose. Our sampling design enabled a high-resolution assessment of drinking water biofilms on small-scale, and the combination of quantitative and qualitative tools for biofilm characterization. This study provides a deeper insight into biofilm formation on building plumbing materials and consequently informs on biofilm sampling strategies.