Wang, MHS and Wang, LK (2022). Cooling water systems, problems, ozonation treatment and ozone demand determination. In: “Environmental Science, Technology, Engineering, and Mathematics (STEM)”, Wang, LK, Wang, MHS, and Pankivskyi, YI (editors). Volume 2022, Number 10, October 2022; pp.57. Lenox Institute Press, Auburndale, Massachusetts, USA.. …………ABSTRACT: Current technology and research concerning the ozonation applications for cooling water treatment are reviewed. The subjects covered in this publication include: (a) cooling systems and problems; (b) corrosion causes, detection, treatment and control; (c) scaling, fouling, deposition treatment and control; (d) microbiological contamination, cooling water treatment, microbiological growth control; (e) ozonation for cooling water treatment including fresh water coolant and sea water coolant; (f) potential cooling water production using ozonation; (g) parameters for ozonation applications, such as residence time, temperature, cycles of concentration, dosage, etc.; (h) testing methods for ozone residual and ozone demand. Special emphasis is directed toward the use of ozonation as a cooling water treatment option and the recommended methods for determination of ozone demand and chlorine demand. Summation includes recommendations for areas of research and calls for further research by the researchers around the world.