SIAAP, the Syndicat Interdépartemental pour l’Assainissement de l’Agglomération Parisienne, is a public organization dedicated to wastewater treatment and water quality across the Paris metropolitan area. It manages the infrastructure needed to transport, store, treat and recover wastewater, operating a network of major facilities and treatment plants, including Seine Aval, Seine Valenton, Marne Aval, Seine Morée, Seine Centre and Seine Grésillons. Through these services, SIAAP helps protect the natural environment and supports the sustainable management of water resources.

The organization invests in improvements to its industrial infrastructure and presents responsible investment as a priority. Its work also includes innovation, environmental monitoring, biodiversity, odor forecasting and public information on water quality. SIAAP shares operational updates and reports, and provides channels for residents to make reports. Beyond its core services, it offers educational activities, school workshops and professional training through La Cité de l’eau et de l’assainissement. The organization also publishes learning resources, recruits for roles across its operations and engages with partners internationally.