Main purpose of this paper was to confirm of results obtained by new method based on bioluminescence technique for determination of susceptibility of materials contacting with drinking water were repeatable. Investigation was conducted during 8 weeks in dynamic conditions using continuous flow reactor UPE. Every week swabbes from tested materials were collected and level of ATP was examined. The results obtained from the surface of tested materials were repeatable and clearly approximate to those obtained from the surface of negative control material (stainless steel, low susceptibility for microbial growth). The level of the ATP on the surface of positive control material (paraffin, large susceptibility for microbial growth) was fifty times higher than that observed on other materials. Presented investigation was the main part of validation process, which in short time will serve to initiate system of complete assessment for materials contacting with drinking water according to Council Directives 89/106/EEC and 98/83/EC requirements.