The reverse osmosis piant permit to obtain through the use of under pressure semipermeable membranes, the dissolution of salts and bacteria contained in water. During the process the water flow is divided in: Permeated, which is the water that after passing through the membrane has a low salt content. Organic substances and bacteria are completely eliminated. Concentrated, which is the high salt content water flow in some cases the salt content can be four times superior to the one contained in the water before treatment. The permeated might contain a residual salt content (between 5-1%) of the initial concentration and can be used in any kind of process requiring a low salt content and bacteriological pure water. If used together with an ion exchenge resin filter, it is possible to obrain water with a conductivity inferior to 0.5 mS/cm.