Electricity costs for pumping account for the majority of operating expenses for water distribution systems. Therefore, researchers and technicians in the water sector have sought to develop techniques that minimize the consumption of electricity in these systems. The large number of elements, which can change state at any time, generates a range of possibilities that makes it difficult to determine which operational scheme is most efficient. Defining the best operating rules for pumping systems is often a complex activity. In this context, the present work presents an optimization model for water distribution systems that combines the efficient use of reservoirs with the best operational rule for activating pumping systems. Using a genetic algorithm, the developed model aims to minimize the operating costs of electrical energy in the systems. The results obtained indicated that, with a better use of the water storage infrastructure, it is possible to reduce the electricity costs of the system as a whole.