The scientific perspective developed in this chapter, is based on a social history of water policies, and diverges from the current paradigms of political studies on water governance. We show that it cannot convincingly be claimed, as did Elinor Ostrom (1990), that everything might be negotiated and resolved at the local level by local actors. One has therefore to examine the social and historical logic underpinning issues that are presented as being new, by paying attention to the social conflicts that have arisen as a consequence of water policies in the American West. From this perspective, it is possible to defend the hypothesis that the current management of water and drought in the American West is conducted via a decentralized and multi-level institutional structure corresponding to an absence of national planning in terms of water use, an instrumental vision of water as a vector of economic growth, and a political field heavily influenced by local and regional forces. To develop this hypothesis, a distinction will be made between three phases of water policy in the western United States (U.S.). The first, which began in the late 19th century and lasted until the 1920s, corresponds to the genesis of the federal policy, whose advocates and structuring effects will be identified. The second phase encompasses the fifty years between 1920 and 1970 and is articulated around the battle between Arizona and California for the water of the Colorado River, the legal resolution of which led to the elaboration of the CAP as the main source of supply for Arizona. This phase makes it possible to shift the focus from the federal to the regional level and to throw light on the third phase, exemplified by the conflict over the quality of water that started in the city of Tucson in 1992. The second and the third phase will be presented in the following chapter. This chapter will present the first phase of the historical process 1890–1929, and will highlight the basis of a long term ongoing process for the making of American water policy. This research based on secondary information and data, on the archives of the protagonists of the conflicts, on the gray literature associated with them, and on interviews with water managers from Arizona constitutes the first part of a larger survey of disputes about water, the logic that underpins them, and their social effects.