Osmosis is defined as a water with low concentration, passes through a semi permeable membrane and forms a equilibrium with water of higher concentration available on the other side of the membrane. The pressure at which this phenomenon takes place is called Osmotic Pressure. For purification of water, the phenomenon is reversed i.e., pressure higher than osmotic pressure is applied to the concentrated liquid which will pass through a semi permeable membrane resulting into a purer form of water/liquid.