Current Status of Drinking Water Quality in a Latin American Megalopolis

(1) Background: Treated water distributed in a Latin American megapolis has been the target of criticism in recent years. During the summers of 2020 and 2021, treated water had a taste and smell of mud in the metropolitan area of Rio de Janeiro city, affecting similar to 10 million people. (2) Methods: To evaluate the SRJ water quality, a comprehensive dataset was analyzed. In total, 194,821 samples were analyzed between 2018 and 2021, corresponding to three parameters (chlorine concentration, n = 67,723; turbidity, n = 55,186; and coliform abundance, n = 71,912). The 92 SRJ cities were analyzed using two approaches according to the relevant law: a quantitative and qualitative approach. (3) Results: In the qualitative analyses, four groups of cities were found (Group A: three parameters analyzed; 49 to 51 cities; Group B, two parameters analyzed, 9 to 14 cities; Group C, one parameter analyzed, 17 cities; Group D, no parameters analyzed, 12 to 16 cities). (4) Conclusions: In 2021, the top ten cities in Group A showed 100% performance in both the qualitative and quantitative rankings. However, several large cities, such as Duque de Caxias and Sao Goncalo, did not have the minimum required number of samples or analyses, which poses serious risks for water quality control and public health.