Explain reverse osmosis
When two solutions of unequal concentrations are separated by a semipermeable membrane which selectively does not permit the passage of dissolved solute particles, i.e.,
molecules, ions etc flow of solvent takes place from dilute to concentrated sides due to osmosis. If a hydrostatic pressure in excess of osmotic pressure is applied on the concentrated side to dilute side across the membrane.
This process is called as reverse osmosis. Thus in reverse osmosis methods pure solvent is separated from its contaminates, rather than removing contaminants from the water.