As a part of the Virtual Plant£ project, computational fluid dynamics (CFD) modeling is applied on full scale water treatment processes to improve water quality, to optimize the existing or test new designs. Single and two-phase flow patterns are modeled for the clarification step (solid-liquid separation) and the disinfection step (ozonation, chlorination and ultraviolet (UV)) applications. As a review of different CFD techniques in water treatment, each process and the respective CFD model are detailed. The objective is the assessment of the process mechanism, in particular the floc transport in the solid-liquid separation, the oxidation by ozone and by chlorine in the corresponding tanks and also the inactivation dose received in a UV process. Includes 20 references, figures.