The report is concerned with modification of the amperometric titration method for chlorine residuals in cooling tower blowdowns or other water systems with a high degree of metal ion content along with other dissolved and suspended solids. The addition of sodium pyrophosphate as a blanket complexing agent appears to remove successfully the heavy metals interferences contributed by Fe and Cu in the blowdown matrix. Procedure recommendations are made to increase the efficiency of both sampling and the actual titration procedure in order to allow a residual determination in the minimum amount of time. Equipment recommendations along with a design of a biamperometric endpoint system which allows greater titration speed along with portability are described.