This Article takes a national view of the modernization of water law. Using Florida as an example, it identifies some of the most important and controversial challenges faced by states. Part II provides an overview of the process of water law reform. As states attempt to improve water management, they have modified their common law water allocation systems with an overlay of statutory law. Often, the process occurs in a piecemeal fashion, resulting in a patchwork of rules -- common law and statutory, old and new. In rare cases -- including that of Florida -- the process may be more comprehensive, one through which states supplement or supplant their common law with modem statutory codes. Part III examines the evolutionary path of Florida, a state that has adopted a generally wholesale reform in modem times. Because this reform took place in 1972 -- at the dawn of the environmental era -- the reform reflects modem environmental and public interest sensibilities. Part IV turns from process to substance, identifying five challenges that plague virtually all states: (1) advancing the public interest while allocating water among competing users; (2) retaining sufficient water in natural streams, lakes, and aquifers to maintain vibrant aquatic ecosystems; (3) ensuring that adequate water supplies will be available for future needs; (4) determining the extent to which managers should "transfer" water from places of relative abundance to places of relative scarcity; and (5) determining the role, if any, of the "free" market 4 in allocating water resources within states.