Utilizing a variety of case studies, this presentation illustrates the investigatory procedures that can be used to understand scale development and relationship to water chemistry, both past and present conditions as well as potential future changes. Diverse water chemistries are represented in the case studies, including low and high alkalinity source water, ground and surface waters, very low and very high organics and inorganics, free chlorine and chloramine disinfection, carbonate and phosphate passivation. The case studies represent both diagnosis of treatment problems as well as prognosis to anticipate both positive and negative impacts of various types of treatment changes. Includes abstract only.