Scholarship on water insecurity has carried over an important insight from studies of food insecurity: Insecurity often occurs in the midst of plenty, and water insecurity is therefore better characterized by inaccessibility than by scarcity. Access to clean, adequate, and reliable water is, however, more challenging to systematize than access to food. Water is fluid and protean, and only when it is safely stored can people pretend to own it. In this paper, I make a case for the centrality of infrastructure - systems of water storage and transport - to water security. Equitable access to water often depends on technologies that protect, filter, and distribute water; it also depends on social arrangements that protect the least powerful from exclusion. I analyse two water infrastructure projects in Ethiopia, one a project to protect village water supplies and the other a large hydroelectric dam. The project to protect springs used by villagers for household water supply had the unintended effect of limiting access to those who could pay fees to a water committee. The dam harnessed water to produce electricity and supply irrigated plantations, but deprived downstream communities of water for farming. Water infrastructure can have far-reaching implications for water access, both for better and for worse. It is often instrumental in securing one group's access to water at the cost of another's.