This paper describes the development and application of computer-based simulators for an existing and an upgraded design of a municipal water production system. Both designs of the system are first described. The key features of the software package used to generate the simulator are presented. The simulators consist of three parts: the graphical interface; the physical models; and, the control logic. The paper then covers the structure and formation of the graphical user interfaces for the simulators. The physical process models of the production systems are laid out in terms of the basic scope and the programming that describes these models. The control logic that is programmed into the simulators is outlined for both plant designs. The five application phases of the simulators are discussed and a summary of the project is given. Includes figures.