In a recent paper (Westerlund et al., 1994) a pump configuration problem was presented and solved using mixed integer non-linear programming methods. The problem was found to be nonconvex. The objective function contained several local optima and global optimality of the obtained solutions could not be ensured, or even reached, in all cases with the MINLP codes. In this paper a concept of binary separable programming will be used in order to obtain the global optimum for the pump configuration problem. The pump configuration consists of centrifugal pumps of different sizes coupled in series and parallel. When the required pressure rise and flow are given the configuration giving the lowest total cost is sought. The total cost includes investment and running costs for the pumps. The capacity regulation can be performed with both speed and throttle control. An optimal flexibility study of the pump configuration problem will also be presented.