Thermal storage is the technology of storing cooling capability generated as chilled water or ice during times of low electrical energy rates for use at times when electric rates are significantly higher. It is in widespread use for large scale comfort cooling as well as many process applications. The use of the technology is promoted by many electric utilities and is acknowledged by Electric Power Research Institute (EPRI) to be important part of load management (reference: EPRI Report EM-5545). Several thousand cooling storage systems are now in operation and hundreds are being added each year. Originally the water sides of these SYstems were treated as conventional closed chillers or ignored completely. Many cases have shown this to be a serious mistake. A review of waterside technology and water chemistry needs particular to these systems is summarized and discussed. The differences between these systems and other more widely known cooling technology are discussed. Fundamental technology as well as operating experiences from both successful and troubled systems are presented. Observations and suggested guidelines for the special chemical needs and methods of approaching operations are presented in this paper.