The "Observatory of Urban Pollutants in Île-de-France/Paris region" (OPUR) research program aims at improving the knowledge on production and transfers of pollutants in urban stormwater and urban wastewater within urban areas. The ambition and originality of the OPUR research program is to create and conduct a field observatory federating different research teams and sewer stakeholders. This observatory aims to be a reference site at the national and international scales. The phase 3 of the OPUR research program (OPUR 3, 2007-2011) was focused on the sources and transfers of pollutants in urban catchments. On the one hand, this phase aimed at examining the quality of urban stormwater (from residential to high densely populated areas). On the other hand, its objectives were also to improve the knowledge on the quality of urban wastewater. This paper describes all studies carried out on urban wastewater and presents the various methodologies applied during the OPUR phase 3. Three tasks were defined: - physical and chemical quality of urban wastewater; - efficiency of different wastewater treatments in regard to chemical and biological contaminants; - and quality of treated effluents and impacts on the receiving waters.