NOVELTY - A real-time oxidation-reduction potential (ORP) in a hot water system is controlled by defining operational protective zones in hot water system; selecting defined zone(s) operable to measure real-time ORP and communicate with a controller; measuring the ORP at the selected zones; transmitting measured ORP to the controller; assessing whether the measured ORP conforms to ORP setting; feeding active chemical species into the water system if the measured ORP does not conform to the setting; and optionally ramping from one of the selected zones to another.    USE - Method of controlling real-time oxidation-reduction potential in a hot water system for inhibiting corrosion in hot water system including fossil fuel fired water-tube or fire-tube boilers; hot water heaters; heat exchangers; steam generators; nuclear power electric systems including light water reactors, pressurized water reactors, and boiling water reactors; marine units; combustion engine and diesel coolant systems; evaporator systems; thermal desalination systems; evaporator systems; paper-making operations including pulping processes and bleaching processes; wafer polishing and planarization processes; combustion gas emissions; fermentation processes; geothermal processes; aqueous organic redox synthesis; polymerization processes; steam ejection equipment; and ancillary devices.    ADVANTAGE - The real-time ORP acts as oxidation-reduction stress indicator for the hot water system which is capable of indicating primary and secondary oxidation-reduction stress events occurring in the system in real-time. The monitoring of the real-time ORP can be used to measure, identify, and assess oxidation-reduction stress demands in the system and can acts as a direct or indirect corrosion process indicator.    DETAILED DESCRIPTION - A real-time ORP in a hot water system is controlled by: (a) defining operational protective zones in the hot water system; (b) selecting defined zone(s) including ORP probe(s) operable to measure the real-time ORP and communicate with a controller, where the ORP probe optionally includes a temperature detector, a noble metal electrode, and a reference electrode; (c) intermittently or continuously measuring the real-time ORP at the selected zones while the hot water system is at operating temperature and pressure; (d) transmitting the measured real-time ORP to the controller; (e) assessing whether the measured real-time ORP or a calculated ORP based upon the measured real-time ORP conforms to an ORP setting, where the ORP setting optionally changes over time; (f) feeding an active chemical species into the hot water system, if the measured real-time ORP or the calculated ORP does not conform to the ORP setting; and (g) optionally ramping from one of the selected zones to another after a triggering event.    DESCRIPTION OF DRAWING(S) - The drawing shows a simplified three-component hot water system.