Does pH affect ORP? The effect of pH is on the activity of the specific disinfectant being used for water treatment. ORP expresses the measure of this activity under the variously interacting water constituents. In this way, it is easier to define and maintain a required disinfection potential using ORP than by using ppm and pH. Chlorine is strongly pH dependent, ozone is moderately sensitive to pH, and chlorine dioxide is least sensitive. Trevor V. Suslow, Ph.D. U.C. Davis