The study performed on behalf of the municipal administration of Milano has the aim of providing a comparative assessment of the evolution of metropolitan sewerage systems face to the challenge posed by the 2000 E.U. Wastewater Framework Directive. It is fundamental that the case studies analyse the technological, economic, management and institutional consequences arising from the shift from an approach dominated by point-source emission standards to restoration of water bodies to a good ecological status. How are other metropolitan areas in Europe facing the new challenge of integrated management at the watershed scale ? The present report analyses the sustainability of the sewerage system developed in the Greater Paris using the methodological framework of the “3E” model developed within the Water21 project (economic, environmental and ethic assessment). : • an assessment of the actual performance face to the environmental challenge and of what is eventually needed in order to meet environmental policy requirements; • an assessment of the viability of the management system with particular regard on the capacity to set aside adequate financial resources for financing investment and keeping assets value over time. • an assessment of the outcomes in terms of affordability and social consensus. The sustainability of the institutional framework is addressed as well.