It is very important to achieve optimal water management in irrigation canal systems. The authors studied optimal water management in terms of water traveling time. First, the authors developed a computer simulation program for varied flow to estimate the water traveling time at any given point for the operation of cross-regulators and offtake regulators. Next, the authors also developed a computer program for unsteady flow in order to quantitatively evaluate the method based on the foregoing. These programs were applied to a long open channel in Thailand. The authors concluded that this method was suitable in terms of water saving and stability in the canal.