This doctoral thesis seeks to analyze the main institutional changes that affected the formulation and implementation of basic sanitation policies in Brazil, more specifically the ones involving water supply and sanitary sewage, and its effects on the Rio de Janeiro state. The main objective from the investigation was to discover if the recent institutional changes, caused by the new National Basic Sanitation Policy, brought social guarantees for the most vulnerable and historically neglected populations. For this purpose, a survey of laws, public contracts and other administrative and legal instruments which determines the conditions under which basic sanitation services are currently formulated and implemented was carried out, with an emphasis on concession processes to the private sector of water supply and sewage services within the state of Rio de Janeiro, previously provided by the Companhia de Águas e Esgotos do Estado do Rio de Janeiro. From the analysis was possible to verify that the changes made in the period between 2011 and 2024 presented more legal security and economic guarantees to the private sector, than social guarantees for the most vulnerable populations, mainly the ones who resides in irregular areas and slums. Beginning a new phase in the historical public-private tension between the attempt to frame the access to basic sanitation as a social right, and the seek for profit by the private sector.