As pressures of climate change, urbanization, and the recognition of environmental water needs become more apparent in river basins around the world, water allocation is becoming a more prominent and important water governance mechanism. Changes to existing water allocations, or reallocation, is the heart of this thesis and is studied through a specific lens of large reservoir projects, or more specifically through the reoperation of existing reservoirs. Reservoirs may be repurposed or reoperated over the course of their lifecycle, in response to such demographic and economic change, and shifting societal water needs. Reoperation offers water managers an adaptation strategy, particularly in situations where new supply infrastructure is unfeasible or undesirable. It is also an opportunity to address, or redress, past water allocation and to improve water equity outcomes. This project focuses reservoir reoperation ‘events’ in three of the world’s iconic, semi-arid river basins: the Colorado River, the Ebro River, and the Ganges. The actors engaged in reoperation events will be studied using institutional analysis approaches and theories, in order to analyze and compare the drivers, mechanisms and actor strategies at play, and their effect on water allocation equity.