Abstract: A process for conditioning recirculated evaporative cooling water in a cooling water system. The process reduces the amount of make-up water required during the operation of this system as compared to conventional water treatment systems. The process includes the steps of determining the pH of saturation. A strong cation exchange media is used in a controlled sidestream and operated so that the pH of the recirculated cooling water is within about a plus or minus 0.4 of the pH of saturation. The system avoids the necessity of storing acid at the water treatment site and also significantly reduces the amount of make-up water required.