The aim of this research was to quantify: (a) the constraints to productivity imposed by the prevailing climatic and weather conditions in the region, (b) the benefits to be derived from irrigation and nitrogen fertiliser, and (c) to better understanding of the mechanisms responsible for the observed responses. In this paper, the actual rates of water use determined from measurements made in two field experiments, based on the line-source irrigation technique (Hanks et al., 1976), are reported for potato crops grown with varying levels of water and nitrogen fertiliser. In a companion paper, the influence of climatic factors on the yield responses to water and nitrogen are described from the same experiments, and crop-yield/water use response functions are derived (Ferreira and Carr, in preparation).