In the first decade of the 21st century, 'hydrosolidarity,' the notion that water management should include considerations of ethics and equity, has influenced international approaches to conducting environmental research and formulating water policy. Since its inception in the 1990s, the term appears frequently across a spectrum of water-related research. It has accordingly permeated discourses and publications on water management. Such rapid proliferation of the concept has helped usher in a wave of transition from conflict management to cooperative efforts between upstream and downstream basin users, as well as a complex paradigm that links both human and environmental welfare. In this paper, we trace the intellectual origins and changing conceptions of hydrosolidarity. We outline some of its applications as well as various reactions to the concept. We close by discussing how the concept can help frame negotiations between riparian states and influence treaty-making and institution-building in river basin settings.