Legal instrumentalism and legal convergence, two legal constructs, describe how American water law has developed over time. A study of early Eastern and Western water law shows that both systems are instrumentalist at their core and evolved to suit pressing developmental needs. Early on in the East, law was created to protect water use for millers, who used mills to generate power. In the West, riparian systems of the East were rejected in favor of a system that met the needs of settlers in more arid environments. Legal convergence is a concept suggesting that law governing various fields converges over time--the legal solution best adapted to solving a problem becomes the dominant approach. Legal convergence, like instrumentalism, supports the notion that in matters of societal importance, such as allocation of water resources, the law will converge around the most effective solutions. This Article explores a number of more contemporary converging, parallel developments in Eastern and Western water law where both regimes have come together despite their fundamental, underlying differences in water rights formulation. These include integration of surface water and groundwater and obtaining full utilization of the resource, elimination of situs of use restrictions, and protection of instream and other communitarian values--each example demonstrates that both regions are adopting similar responses to reach a common goal to utilize water resources to meet as many water needs as possible. This Article predicts that the next major change in Eastern and Western water law will be a convergent approach to water triage during episodes of regional water shortage.