This paper examines the method of using project irrigation requirements (PIR) in the design and rehabilitation of small-scale smallholder irrigation systems within multi-sector and dynamic river basins. The paper argues that if the PIR equations are used formally and conventionally without sufficiently accounting for changing demands for water in semi-arid river basins, they can lead to irrigation designs that over-prioritize water for individual irrigation systems and as such be labelled "irrigation-centered". Features of a modified planning and design methodology are suggested, and the implications of this dualism in approaches (irrigation-centered or resource-centered) for basin management, livelihoods, conflict mediation and formal irrigation rehabilitation projects are explored.