As a complement to commercial hydrodynamic software to replicate drinking water distribution systems, a model for biological contamination was developed. The model is called the Biofilm contamination model (BioCon) and is constituted by transport and biofilm models that capture the most important features using a system of partial differential equations. In addition, a numerical solver that implements the biophysical models and visualizes the resulting concentration of contamination over time in the system has also been developed. BioCon is designed to be able to handle a wide range of biological agents and environmental prerequisites through parameter settings. Two pathogens, Escherichia coli and Cryptosporidium spp., act as pilot agents throughout this report, and extra attention is paid to their specific behaviour. In addition, a suggested parameterization for E. coli is presented. The parameterization is based mainly on data published in the literature but also on data from preliminary laboratory experiments conducted within this project. The model design of the main components, such as transport, attachment/detachment, biofilm development, and the influence of temperature, disinfectants, and nutrients, are constructed to generate behaviour in accordance with numerous pre-existing experimental findings and theoretical models. In this sense, the core behaviour of BioCon has been successfully verified, at least in part, which is presented here. However, a quantitative validation of the entire concept of BioCon, including parameterization for a specific agent and the environmental settings, in comparison with experimental observations of a corresponding system has not been conducted and is suggested as a future study.