Water is among the most shared resources on earth. Close to half of the earth’s land surface lies within river and lake basins that cross international borders, while an estimated two billion people rely on groundwater. Much of this groundwater is stored in aquifers that extend across national boundaries. These shared reserves link livelihoods, community well-being, and ecosystem health. As climate change, population growth, and economic development intensify the pressure on these systems, there is an increasing need to manage groundwater equitably and sustainably.