Operating Pressure - the range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function.
Osmosis - a process of diffusion of a solvent such as water through a semipermeable membrane which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentration solution.
Oxidation - a chemical process in which electrons are removed from an atom, ion or compound. The addition of oxygen is a specific form of oxidation, while the rusting of iron is a slow form.