Measuring the oxidation–reduction potential of important oxidants in drinking water

Oxidation–reduction (redox) reactions can affect drinking water treatment and distribution in significant ways. Measurements of oxidation–reduction potential (ORP) in water reflect the tendency of major constituents in the water to accept or lose electrons. Although ORP measurements are valuable and can provide useful information toward protecting public health, they are not widely undertaken by the drinking water community for a variety of reasons. The objective of this research was to determine the effect of five oxidants commonly used in drinking water treatment as well as the effect of pH on measured ORP. Results showed that the ORP of each oxidant system increased with increasing oxidant concentration to a maximum. The ORP also decreased with increasing pH. Water treated with chlorine and chlorine dioxide had the greatest ORP followed by water containing monochloramine and permanganate and water containing only oxygen. Duplicate ORP measurements revealed some inconsistencies with redox electrode measurements.