This research utilizes Social Network Analysis to examine the ownership and management structures of the five largest private sanitation groups in Brazil, with a specific focus on the state of Rio de Janeiro following the 2021 privatization wave. The study identifies a high degree of oligopolization and financialization, revealing that three of the top five groups share common global institutional investors, including the Sovereign Fund of Singapore, the Canada Pension Plan Investment Board, and BlackRock. This interconnectedness creates what the authors term a giant component in the proprietary network, potentially undermining market competition. The analysis of corporate directors reveals a small-world effect characterized by interlocking directorates and a revolving door phenomenon between the public and private sectors. Key individuals, such as former high-ranking government officials and academics from institutions like the Getulio Vargas Foundation, serve as strategic bridges that align corporate governance with financial logic. Quantitatively, the study maps 245 shareholders and 972 connections in the ownership network, alongside 929 actors in the directorial network, demonstrating how these social and capital ties consolidate corporate power over essential resources like water and sewage services.