The historical trajectory of the Maipo River basin offers critical insights into current and future challenges in Chile's internationally famous model of water management. We highlight the legal dimensions of the trajectory, looking beyond the 1981 Water Code and water market debates to some of the underlying principles of Chilean water law that shape river management. In particular, we focus on a legal-administrative rule that splits rivers into multiple, independently managed ‘sections’ – a policy that has received little attention despite posing a prima facie contradiction to the goal of integrated water resources management. We demonstrate that, despite government officials’ insistence that this policy is merely an ‘artificial’ administrative tool, river sectioning has significant material, discursive, and socio-political consequences for water governance. We highlight three emerging issues: (1) tensions over section boundaries, (2) the institutionalisation of a ‘right to leave the river dry’, and (3) ongoing struggles to establish formal vigilance committees in the lower sections. Far from functioning as a legal simplification, river sectioning is complicated and contentious and demands more attention in policy and research. We conclude by considering possible solutions aligned with efforts to move toward more coordinated and equitable water management in this crucial basin.