Information on the water footprint of pasture-based beef production is useful for optimizing the allocation of groundwater to crop and livestock production. The objective of this research was to determine the effect of including legumes on three water footprints of grass-based, beef stocker grazing systems with respect to observed and total (observed plus predicted from hay production) liveweight gain (LWG). Water inputs for the calculations included total or effective rainfall, total or corrected drip irrigation, and water directly consumed by the steers. When including rainfall in the calculation, water footprints were 16.2 to 40.5 vs. 1.7 to 8.6 m3 kg−1 LWG when including groundwater only. Inclusion of legumes into the system reduced each water footprint with respect to observed LWG in all years (P ≤ 0.01). When total LWG was considered, the water footprint was lower in the grass-legume system if rainfall (total or effective) was included (P < 0.01) but greater if the evaluation was restricted to irrigation and drinking water as inputs (P < 0.01). Overall, including legumes reduced the water footprint of beef LWG, largely because of greater rates of gain from the greater quality forages. Quantifying water use in the stocker phase adds a missing component in evaluating limited resources in the beef production life cycle. Managing legumes in mixture with warm-season grasses and as a protein bank can increase the efficiency of beef grazing systems, resulting in an overall lower water footprint for animal weight gain.