The reuse of wastewater aims to mobilize and treat, for certain uses and under certain conditions, water that has already been used. Rather than discharging wastewater into the natural environment, this practice aims to recover it by replacing the mobilization of water withdrawn from the environment [van Loosdrecht and Brdjanovic, 2014]. By moving from a linear logic of the mobilization and use of water to a circular approach, the objective pursued is to reduce the pressure, qualitative then quantitative, on the resources while limiting, as far as possible, the usage conflicts. It is in fact a question of passing from a simple competitive mode which strongly mobilizes resources, to a complex mode, known as “circular”, of putting in complementarity of uses. This approach initially mainly concerned agricultural uses insofar as agricultural needs represent the majority of the water mobilized, including developed countries [UN Water 2018]. Cities integrate specific issues that are characterized by significantly different options from those that can be found in rural areas. In the city, the recovery of wastewater has both material aspects (water, nutrients, critical metals, biopolymers, etc.) and energy aspects (recovery of heat from the networks, production of energy by biological means and /or thermal,…) which should be integrated on an appropriate scale according to the problems addressed (housing, building, district, city, territory or hydrological basin). To study the conditions under which REUSE can develop and be implemented in a safe and sustainable manner, research is needed [Ait-Mouheb et al., 2018]. If it represents an opportunity in certain territories where wastewater can be mobilized, it is also necessary to underline the limits of this practice in territories where the wastewater discharged into the environment is necessary to maintain the low water levels of rivers and rivers, or where soils may be affected, for example, by the salinity of these waters. In addition, studies of the social, economic and environmental dimensions differ significantly depending on the uses envisaged and the situations considered. To meet these challenges, the REUSE network of INRAE (cf. www6.inrae.fr) proposes to adopt a multidisciplinary and multi-scale approach by mobilizing not only the disciplines that can be considered as falling within the field of technologies and environmental engineering but also all of those relating to the human and social sciences, economics, legal, and participatory sciences.