Drinking water quality may change during transportation through the distribution network. There can be observed tendency of a decreased organoleptic quality and microbial regrowth. The one of the main reasons for bacterial regrowth is due to depletion of disinfectant residual and/or sufficient nutrient concentration in bulk water. The growth of microorganisms mainly occurs on the inner surface of pipelines forming biofilm, i.e. biological cover. Bacterial regrowth may causes appearance of taste and malodor, turbidity, loss of residual chlorine and increased risk of pathogens survival. Several in the same time occurring chemical and microbiological reactions influence these processes. The interaction between different factors in the networks is very complex. The hydraulic model linked with Multi-Species eXtension platform (Shang et. al, 2007) could be used to predict drinking water quality and select strategies for combating quality problems and to predict when and where water quality events are likely to occur rather than responding to events after they occurred.

The verification of the models in the full-scale is difficult to accomplish due to the influence of many factors not included in the models (e.g. corrosion products, particles) and problems with the sampling e.g. obtaining biofilm samples from the buried pipes. Therefore biofilm models made from stainless steel and PVC like Propella® are used.