A major objective of plant breeding programmes in semi-arid conditions is the selection of more drought-tolerant plant material. An irrigation system has been developed to assist in water use and drought tolerance screening studies of potato genotypes in the confined space of a rain shelter. The line-source principle was used as a departure point for the design of an irrigation boom, attached to the roof structure of a rain shelter. Five water regimes were achieved by using nozzles that differed in discharge rate and three genotypes per rain shelter were evaluated simultaneously. Crop production functions could be established for the different genotypes. The system shares some disadvantages of the typical line-source, such as the simultaneous irrigation of all plots and water treatments are not randomised. The main advantage above traditional plot systems, which would use drip or micro irrigation under rain shelters, is the ease of management.