In boiling water nuclear reactors the numerical and experimental study of flowing films is relevant to the safety thermal analysis of the cooling channels. In particular, measurement of velocity profiles in thin liquid films is extremely useful for validation of best-estimate system codes as well as Computational Fluid Dynamics (CFD) codes. However, the most common techniques for velocity profile measurement are based on acoustic or optical principles, which exhibit intrinsic inaccuracies when dealing with thin films. An alternative technique for velocity profile reconstruction in thin water films is proposed and validated. Water films are investigated using a flush wall film conductivity sensor, and a high-speed camera. The film sensor measures the film thickness over a spatial matrix of 96 x 26 measurement locations with a spatial pitch of 2 mm. A conductive tracer is injected into the film, with the film sensor providing both the film thickness and tracer concentration integrated over the film thickness. The measured tracer concentration at the time when injections are over is used as initial condition for running an advection-diffusion 2D simulation for each liquid layer of the film. The simulations from all the layers are averaged so that they are comparable to the measurements of the conductivity sensor. For each layer, the unknown advection velocity is determined with an optimization algorithm, which minimizes the difference between the simulated and measured averaged concentration. The velocity profile across the measured film thickness is then reconstructed from the advection of the single layers. VOF simulations are run to further validate the presented methodology and its underlying assumptions.