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.
A Reverse Osmosis plant comprises of membranes made of polyaaid, etc. The spirally bound membranes are subjected to pressure to complete the process of Reverse Osmosis. They are typically used whenever salt removal or deionization is required. Reverse osmosis removes more than 97%-99% of the total dissolved solids along with organics, bacteria and other particulates.
Reverso Osmosis is becoming more and more popular viz a viz ion exchange process because of input TDS restrictions in ion exchange and ease of operation.