Reverse Osmosis is a separation process, which involves the passage of liquid from the lower concentration of dissolved substances to that of a higher concentration, when the two are separated by a semi permeable membrane. Thus, pure water is produced by screening out dissolved salts and other contaminants. 

Reverse Osmosis Membrane is made of Semi permeable membranes, made of cellulose acetate or aromatic polyamide, having pore size of 0.0001 microns in diameter. These can filter out most of the inorganic contaminants, microscopic parasites including viruses, which may cause serious health hazards.