The abbreviation R O typically refers to Reverse Osmosis. Reverse Osmosis is a water purification process that uses a partially permeable membrane to remove ions, unwanted molecules, and larger particles from drinking water.
In this process, pressure is applied to overcome osmotic pressure, a colligative property that is driven by chemical potential differences of the solvent. The result is that the solute is retained on the pressurized side of the membrane, and the pure solvent is allowed to pass to the other side. This method is widely used for desalination, wastewater treatment, and the production of high-purity water for various industrial applications.