Reverse osmosis is a separative process allowing the extraction of pure water from a salt solution by diffusion through a thick film membrane. A pretreatment is necessary to avoid fouling phenomena due to suspended solids or chemical scaling. That pretreatment includes two stages: fine filtration and softening or chemical treatment of the water to be deionized. The water then feeds the reverse osmosis unit at a pressure of about 16 to 20 bars to produce 75 % demineralized water and 25 % brine that will be rejected into the natural environment without any special treatment. A deionized water buffer storage tank will allow the optimization of the reverse osmosis unit size and its daily working time.