All energy scenarios show a shift toward an increased percentage of renewable energy sources, including biomass. This study gives an overview of water footprints (WFs) of bioenergy from 12 crops that currently contribute the most to global agricultural production: barley, cassava, maize, potato, rapeseed, rice, rye, sorghum, soybean, sugar beet, sugar cane, and wheat. In addition, this study includes jatropha, a suitable energy crop. Since climate and production circumstances differ among regions, calculations have been performed by country. The WF of bioelectricity is smaller than that of biofuels because it is more efficient to use total biomass (e.g., for electricity or heat) than a fraction of the crop (its sugar, starch, or oil content) for biofuel. The WF of bioethanol appears to be smaller than that of biodiesel. For electricity, sugar beet, maize, and sugar cane are the most favorable crops  If a shift toward a greater  contribution of bioenergy to energy supply takes place, the results of this study can be used to select the crops and countries that produce bioenergy in the most water-efficient way.

Source: PNAS

Gerbens-Leenes et al., conclude by saying that

The scientific and the international political communities
promote a shift toward renewable energy sources, such as
biomass, to limit the emission of greenhouse gases. This study has shown that biomass production goes hand in hand with large water requirements. There are already reasons for profound concern in several regions and countries with limited water resources about whether the food and fiber needs of future generations can be met. If a shift toward a larger contribution from bioenergy to total energy supply takes place, results of this study can be used to select the crops and countries that (under current production circumstances) produce bioenergy in the
most water-efficient way.