The article discusses the role of social participation in the development and implementation of three water and sanitation plans for the city of Belem, capital of theState of Para, Brazil: the Belem 2000 plan, which was launched in 1980; the Master Plan for Water Supply and Sanitation for the Belem Metropolitan Region, developed between 2004 and 2006; and the 2015 Municipal Basic Sanitation Plan. My research, based on a qualitative approach, found that the role of social participation in the plans was strongly influenced by the underlying forms of rationality of these plans. In the normative rationality that predominated in the plans drawn up in 1980 and 2015, social participation was limited to the participation of technicians, also due to legal requirements. In contrast, the strategic rationality of the plan developed between 2004 and 2006 introduced a dialogue between different social sectors, which resulted in processes of community-based validation and social legitimation of the plans. The results show that merely tokenistic participation, as promoted by normative rationality in public policy, tends to negatively affect social participation, especially in a context like Belem’s during the period of the study, which was marked by the promotion of private investment in water and sanitation services.