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Lamella gravity settlers are often used in water treatment to make sedimentation tanks more cost-effective. Effective surface area for settlement is increased by the inclined plates giving such systems a smaller footprint than the conventional tanks. In this paper a numerical model was used to simulate the dynamics and flow structure of a rectangular sedimentation tank for potable water through a multiphase approach, using computational fluid dynamic (CFD) methods. Two configurations have been examined, one with a system of inclined parallel plates (lamellar settlers) and another with a conventional design, in order to evaluate the influence of lamellar settlers in the process efficiency. Unlike most of the previous numerical investigations which studied the lamellar settlers separately, the present numerical approach studies the whole sedimentation tank with a full scale system of inclined parallel plates. The momentum exchange between the primary and the secondary phase (particles) is taken into account, using a Lagrangian method (discrete phase model) with two-way coupled calculations. Contours of stream function, velocity and concentration are presented, as well as the velocity and concentration profiles for the inclined plates. The results show that the lamellar settlers influence the flow field and increase the sedimentation efficiency by 20% in comparison with the convectional design. [ABSTRACT FROM AUTHOR]