This paper explores the specific technical challenges to both engineer and simulation tool through the experience of the Portland Water Bureau and Advantica Stoner. Portland maintains a model of more than 30,000 elements, but the striking feature is the inclusion of over 600 pressure regulators supplying 165 pressure zones. Understanding the real system's behavior is quite difficult, so a hydraulic model is a great operational and planning aid. However, simulating a system with this degree of pressure regulation presents challenges to current modeling technology. The challenge was attacked from various angles: field and bench testing; examination and adjustment of how facilities are represented in the model; and enhancement of the simulator. The experiences dealing with this complex system are discussed. Modeled behavior and expected behavior are compared, and a summary of bench test results on the pressure regulators in use is presented. Includes figures.