The optimal design of water distribution networks is a complex problem even in its simplest formulation, where only the maintenance of a minimum pressure is required. This paper compares the best solutions obtained using different optimization algorithms: the BONMIN Branch and Bound algorithm, which directly tackles the MINLP (mixed integer non-linear programming) formulation, and two heuristic algorithms, i.e. GHEST (genetic heritage evolution by stochastic transmission) and an island parallel implementation of the multi-objective algorithm NSGA-II. In addition, the best solutions are compared with the actual diameter configuration of the network in terms of cost and of hydraulic behaviour. The three algorithms are applied to the hydraulic model of Modena water distribution network that takes into account the main pipes.