The measurement and control of oxidation-reduction potential (ORP or REDOX) is critical to the safety and comfort of the occupants. ORP measurements are necessary to monitor the disinfection process (or reaction) by chlorine or other oxidants is still in process. If the ORP is too low, it is an indication of high amounts of contaminants in the water. Pool and spa environments measure ORP continuously in larger commercial control systems but may also be measured by a service technician with grab-sample methods. Common performance challenges can be mitigated with the optimal sensor design, in particular the reference junction design, housing material, and sensing element.