Two Brazilian cities in the southern region of the state of Minas Gerais have engaged in public debate on the exploitation of their mineral waters by the private sector, with prompted contestation from organised civil society and other actors to the governmental decision. This study aimed to analyse that public debate using the theoretical-methodological approach of argument analysis within critical discourse analysis (CDA). A news report and a legal text formed the corpus of analysis as representative of ongoing argumentations because these discourses can influence public policy decision-making. The results showed how the controversy is rooted mainly in the conflict of values between two parties – on the one hand, the concern over sustainability and environmental conservation, cultural identity, the concept of water as a common good, and the defence of public participation and, on the other hand, the predominance of values focused on economic development and the efficiency of financial management of resources.