Drought stress restricts sugar beet growth and yield formation. For the development of adapted varieties, reasons for high water demand in certain growth periods and for genotypic differences in water use efficiency (WUE) were investigated. In 2019 and 2020, different drought stress periods were simulated in pot trials in the greenhouse with four sugar beet genotypes by reducing the water supply to 50% of the water holding capacity. With unlimited water supply, water consumption developed in parallel to the growth rate. This indicates that water demand is driven by growth rate. Therefore, early drought stress in the period with highest growth rate caused strongest yield reductions, which could not be compensated later in the season. Unlike sugar yield, water consumption differed among genotypes, resulting in genotypic differences in WUE. However, no relevant genotype by water supply interaction occurred, giving no indication for drought tolerance of the genotypes with high WUE. WUE is rather determined by the sugar yield potential of a genotype than by water supply. Therefore, sugar beet genotypes should be selected for their sugar yield potential when breeding for environments with varying water supply.