Through time a water distribution network's carrying capacity is reduced as material collects on pipe walls. The impact varies with each pipe in the system and occurs at an unknown rate. Periodic pressure tests may be performed with the resulting data used to determine the pipe roughness coefficients, valve losses, and pressure regulating valve settings. To eliminate the need for trial and error techniques, a calibration methodology is presented which determines the optimal values of these terms while simultaneously considering more than one pressure test. The solution procedure is based upon concepts of optimal control and the theory of reduced gradients. The technique links an optimization model and a network simulator which allows larger problems to be solved in reasonable times. By doing so the model is easily applied by design engineers. Improved coefficient estimates will result in more accurate simulation which will assist in operating systems and in making decisions for rehabilitation, replacement, or expansion of pipe networks.