This study focuses on the settling step (solid liquid gravity-driven separation) in conventional drinking water treatment plants. A numerical model is presented here to simulate settler performance. The model takes into account the presence of sludge by adding a one-dimensional settling source term. Before applying the computational fluid dynamics (CFD) tool on the pilot settler, the method was first tested with the well-published experimental batch settling results (the Kynch tests). An advection equation was solved by a finite difference method and validated experimentally. The comparison between batch and numerical settling curves gave a sludge parameter estimation of the Takacs settling velocity model. The coupling of this model with CFD was implemented in ESTET-ASTRID(R) software. Initial results on an industrial application demonstrate the model efficiency. A lab-scale pilot dedicated to the validation of the CFD model is described and hydrodynamics results on clear water are presented in this paper. Velocities measurements are obtained by PIV technique in order to obtain a complete velocity mapping in the tank.