A burgeoning scholarship has taken seriously the use and management of the world’s freshwater as a site of critical investigation while highlighting the contribution of science and technology studies in making the infrastructural life of water visible. However, studies say little about the calculative terms of the decision-making process involved in infrastructural appraisal and are often taken for granted as something inevitable. This article examines the unexpected and remarkable role that cost-benefit analysis played in governing Iran’s democratic future through the assembling of a dam in the mid-twentieth century. Indeed, cost-benefit analysis traveled the world by flows of water. I investigate the ways in which the calculation of risk generated by the device of cost-benefit analysis of neoclassical economics became over several decades the most influential language for explaining and organizing the relationship between humans and nature in southwest Iran. The waters of the Dez River and other major rivers of the world shaped the building of large-scale infrastructural projects around dams, but they were simultaneously entangled with the production of economic information about the costs and benefits to the local, making possible the development of new methods of governing democracies in terms of risk. US-based government aid agencies, institutions of global economic governance, private American investors, engineers, and agricultural scientists converged in a small corner of Iran to transform the region, its water, and its farmers into a laboratory of grass-roots democracy for a profit
