 Hydropower accounts for approximately 16% of the world's electricity supply, with some debate over whether it is merely an in-stream water user or whether it also consumes water. This paper provides scientific evidence that hydroelectric generation is often a significant water consumer, with its blue water footprint, water evaporation, for man-made reservoirs, being equivalent to 10% of the blue water footprint of global crop production in 2000. Furthermore, the total blue water footprint of hydroelectric generation in the world is likely much higher when considering the fact that this study covers only 8% of the global installed hydroelectric capacity. Hydroelectric generation is therefore a significant water consumer, with great differences in water footprint among hydropower plants, due to differences in climate and the area flooded per unit of installed hydroelectric capacity. To ensure sustainable use of water resources, water footprint assessments should be included in evaluations of new hydropower plants and existing hydroelectric dams, so that the consequences of the water footprint of hydroelectric generation on downstream environmental flows and other water users can be evaluated.