Most difficulties in water negotiations are due to rigid assumptions about how water must be allocated. When countries (or states) share boundary waters, the presumption is that there is a fixed amount of water to divide among them, often in the face of ever-increasing demand and uncertain variability. Such assumptions lead to a zero-sum mindset, with absolute winners and losers. However, when parties instead understand that water is a flexible resource and use processes and mechanisms to focus on building and enhancing trust, even countries in conflict can reach agreements that satisfy their citizens’ water needs and their national interests.