Abstract: Systems and techniques of treating water can be performed by utilizing characteristic functions to generate a control signal to regulate addition of a disinfecting species to the water. The characteristic functions, which can be a dynamic chlorine redox relationship between the oxidation-reduction potential and the concentration of free available chlorine species in the water, can be mapped, at least in part, by a corresponding sets of measured process parameters of the water. A triggering condition can initiate change and identification of the characteristic function.