Reverse Osmosis System 500LPH When two aqueous solutions of different concentrations are separated by a semipermeable membrane, naturally occurring osmotic pressure forces dilute solutions into the concentrated solutions this natural phenomena is called osmosis which continuous until equilibrium between the two solution is reached.The flow's natural direction can be reversed by applying pressure greater then osmosis pressure to the concentrated solutions. This process of reversal of solvent flow known as "Reverse Osmosis" (RO).