In France, there is a recurrent debate on the choice of organization, management modes and regulation of the water services. They are local monopolies which may be directly managed by the municipality or delegated to a private operator. An econometric analysis of cost for the drinking-water supply services gives crucial information on the potential gains in terms of network performance and resource management. A counterfactual comparison of the costs of the management modes (public/private) shows the differences in efficiency and the existence of an informational rent for private operators.