RESUMEN
Modern sewage systems were once a cutting-edge innovation that transformed how people consumed water. This article examines a debate among a group of British engineers involved in a sewage system scheme in late nineteenth-century Cairo, when Egypt was under British colonial rule. Assessing the project's economic feasibility, the engineers came to different conclusions regarding the future users of the system and, by extension, future consumers of water. Reconstructing the debate sets up a dialogue between engineering and economics to show that engineers could be economists too. This debate represents a type of economic analysis that public works engineers pioneered in the mid-nineteenth century. The engineers reached novel conclusions by centering consumers as the foundation for calculating economic realities.