Ideas on what is best practice to provide more people in rapidly growing low-and middle income cities with adequate water supplying services have changed during the 20 th century.By applying a frame-theoretical approach, this article analyses institutional choice in Ghana´s urban water sector. Special attention is paid to two major events: first, the establishment of the state water utility, Ghana Water and Sewerage Corporation, in 1965, and secondly the reform process in the 1990´s and early 2000´s which aimed at private sector participation in urban water management. By unravelling the arguments and taken for granted assumptions underlying the two reforms, the article shows how the perceived space for policy alternatives available to decision makers at a certain point in time has been largely constrained by the dominant frames in a particular historical context. This conclusion is supportive of the argument that rationality is a highly contextual and time dependent concept.