This paper focuses on the operational control problem of determining the optimal pump operation policy for a given distribution system. The optimal pump policy is defined as that schedule of pump operations that will result in the lowest total operating cost for a given set of boundary conditions and system constraints. In the current study, the operational control problem is divided into two subproblems. The first subproblem involves determining the optimal tank trajectory for each tank in the system. The optimal tank trajectory is defined as that series of tank water levels over time which result in a minimum total operating cost. The second subproblem involves determining the specific pump operations required to produce the optimal tank trajectories.