In the field of reverse osmosis (RO) there are several theories from which mathematical models have been developed, allowing for the simulation of processes and the prediction of results. This study used the model developed by Slater and Col, based on the solution-diffusion model for the simulation of RO processes. It was developed with an M20 RO Lab Unit made by DOW DANMARK SEPARATION SYSTEMS and uses a pair of flat membranes of HR 98 PP type, also made by DOW DANMARK A/S SEPARATION SYSTEMS. The results obtained are within the expected range for the volume flows and permeate concentrations under study. All the relevant constants in the model were determined, and were found to be in agreement with the expected results. The solute used was potassium chloride (KCI) and the dissolvent was distilled water, with concentrations ranging between 200 and 3000 ppm. Feed flows were in the range of 4.80 y 8.18 L/min, while the working pressure varied between 5 and 20 bar.