This article is based on an historical approach to the management of sanitation in the contemporary city. Flow and network are concepts that characterised modern cities, in terms of relation systems, urban functionalities and space conflicts. Between these flows, there are those unequivocally related with the modernization of the city electricity i. e. but also those garbage collection and sanitation that established conflicts between different types of interests. This kind of conflicts are particularly evident in the case of improvement of sewers, which reshaped the relations between public and private, in terms of spaces, social structures and political approaches. The case study of Barcelona, with its hierarchal but also relative disrupted organization, show how the adoption of a system of tout-à-l’égout, after a long debate throughout the XIX century, represented the beginning of a model for many aspects unsustainable.