This article analyses three key moments in the historical development of urban wastewater infrastructure and points to the important role that professionals, and particularly engineers, play in these transformations in relation to public issues and concerns over wastewater. The article uses historical documents and interview data to illustrate the work of professionals, as well as suggesting more specifically that professionals have the capacity to translate public concerns into material solutions—in this case, infrastructures. By combining and developing Laurent Thévenot’s pragmatic sociology and Andrew Abbott’s sociology of professions to understand the historic role of professionals in urban wastewater planning, the article reveals a growing concern with ‘green’ justifications in this area, and how these justifications both enable and constrain professional work on specific infrastructures.