In Iran under the second Pahlavi era, the question of water was tied not only to technical and economic dimensions but also to the political, institutional, and discursive transformations of the state and its development model. This article examines how water was redefined in the documents of the development plans, and how it was gradually transformed from a natural resource with social and economic functions into an object of technical intervention, economic exploitation, and centralized state governance. The study hypothesizes that the predominance of a growth-oriented and instrumentalist approach to development, interacting with the expansion of specialized institutions and legal mechanisms, strengthened state intervention in the management of water resources and pushed social and ecological considerations to the margins of water policymaking. Drawing on a genealogical approach and a historical analysis of the documents of the First through Fifth Development Plans, water-related legislation, and official reports, the study investigates changes in water policy between 1948 and 1977. The findings show that these changes unfolded as a gradual, multi-stage process. In the First and Second Plans, technical knowledge of water resources and the expansion of surface and groundwater exploitation were linked to agricultural objectives and economic growth. In the Third Plan, the expansion of specialized institutions and legal mechanisms strengthened the foundations for organized state intervention. In the Fourth and Fifth Plans, with the enactment of the Water Nationalization Law in 1968 and the expansion of large-scale hydraulic projects, the legal and institutional centralization of water governance intensified. This trajectory can be analyzed within the framework of the expansion of instrumental rationality and the emergence of elements of a hydraulic state in contemporary Iran.