Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to remove ions, unwanted molecules and larger particles from drinking water. A process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure. Reverse Osmosis is the most effective and economical way to provide your family with high quality drinking water. Reverse Osmosis is the process by which water molecules are forced by your household water pressure through a semi-permeable membrane. Contaminants are rinsed to the drain while your high quality drinking water is stored in the holding tank.