The Oxidation Reduction Potential (ORP) is applied for controlling the chemical and biological reactions. It means, by the help of ORP the tendency of reactions for occurring in aqueous solution are measured. The ORP measurement has been used in variety of applications especially, water and wastewater treatment e.g. cyanide detoxification, advanced oxidation processes (production of hydroxyl radicals: fenton), water disinfection and etc. By measuring the ORP during the reaction, the end time of reaction, the required concentration of reactants and optimum conditions be determined. In this study, the use of ORP in most common reactions in water and wastewater industries are investigated.