Reverse Osmosis is a process whereby liquid water molecules are separated from the rest of a solution. The boundary layer is a semi-permeable membrane with a mixture of various elements in water on the one side and pure water on the other side.
The semi-permeable membrane has the unique characteristics that allows the tiny water molecules to pass either way but keeps out the larger ones i.e. : pesticides, lead, asbestos, germs, chloride, soluble solid matters, arsenic, etc.
The application of pressure on the raw polluted water forces the pure water molecules through the membrane and the unwanted molecules are left on the pressure side. As the salts build up against the membrane and the pressure side, the rate of passage of water (flux) decreases gradually. However, allowing the concentrate to continuously drain and keeping a new water supply flowing across the membrane establish an equilibrium. This process is now continuous and could carry on forever if there would be no scaling, blinding or damage to the membrane.