A recent definition of biological stability implied that no changes should occur in the concentration and composition of the drinking water microbial community during distribution (Lautenschlager et al., 2013; Prest et al., 2016a). Production of biologically stable water is a feasible solution: this is usually achieved by removal of growth-limiting nutrients and/or addition of residual disinfectant. Nevertheless, unwanted bacterial growth in distribution networks can occur, even if the treated water contains chlorine residuals (Nescerecka et al., 2014). Most of the methods intended for the assessment of biological stability are based on determination of organic carbon, namely, assimilable organic carbon (AOC) and biologically degradable organic carbon (BDOC). Although these are well-established standardized bioassays, they provide incomplete information if inorganic elements such as phosphorus are limiting. A deficiency of inorganic elements can limit bacterial proliferation, or, in turn, the presence of inorganic compounds in sufficient amount would promote growth of specific autotrophic microorganisms and heterotrophic bacteria if organic carbon is available. Thus, there was a need to find an approach to evaluate biostability in a water supply system, where various nutrients could limit bacterial growth. The objectives of this study were: (i) to investigate changes in bacterial concentrations during an extended time period in a full-scale drinking water network (DN) in order to investigate temporal biological stability; and (ii) to assess a new approach for drinking water biological stability assessment to identify growth limiting/promoting factors in the system supplied from surface and groundwater sources.