Energy and water systems are increasingly intertwined, particularly in regions where desalination represents a major flexible load. As the share of renewable energy increases, additional system flexibility becomes essential, and the desalination sector can provide part of this flexibility through adaptive operation and water storage. This paper develops an economic, game-theoretic framework for energy-water coordination that models a power service provider setting time-varying prices and desalination plants optimizing their desalination and storage decisions as a result.