Static models used in economics and ecology ignore dynamic processes at work in both human and natural systems. In the case of water management, whether for quantity or quality, static models fail to connect changing human demands on water systems with changing supplies due to short-run climate variations and long-run climate change. Water markets provide a way of connecting human demands to nature's supplies through prices, which signal values and scarcity. For water markets to make this connection, water rights must be well-defined, enforced, and tradeable. When they are, entrepreneurs are able to meet old and new demands on water ecosystems in novel ways, as examples in this essay illustrate.