This manual is a source document for utilities that are considering a coagulant changeover. It is intended to provide an appreciation of what must be considered for a successful changeover based on the input of U.S. and Canadian utilities (Chapters 1 and 6). New regulatory requirements will likely have the broadest and most substantial impact on primary coagulant use (Chapter 3). The Interim Enhanced Surface Water Treatment Rule (IESWTR) and Stage 1 Disinfectant and Disinfection Byproducts Rule (Stage 1 DBPR) will make finished water requirements more stringent to address microbial removal and the impacts of disinfection. Enhanced Coagulation and/or other operational and treatment practices will be used to achieve these requirements. The science of coagulation (Chapter 4) requires a special focus to address the intricacies of coagulation chemistry. The manual provides a step-by-step methodology to conduct a coagulant changeover using a detailed protocol (Chapter 5) -- background, executive summary.