Alfalfa (Medicago sativa L.) can enhance the supply of nutritious forage when interseeded into semiarid native grassland. Alfalfa is a high water-using species; therefore, a possible trade-off between soil water depletion and nutritive value merits study. We determined the effects of interseeding three alfalfa cultivars at two densities on crude protein (CP) and digestible organic matter (DOM) accumulations, the water footprint (WF, m3 evapotranspiration kg−1) of CP and DOM accumulation at two row spacings, and the marginal cost (MC) of such trade-offs. Nutritive values and accumulation of CP and DOM for mixtures with alfalfa planted at 36- or 71-cm row spacing did not differ in 2018 (P >.05), as both spacings reduced the WF over grass only (P <.0001). Alfalfa presence reduced the WF (P <.001) with respect to CP and DOM accumulation from 20.17 and 3.07 m3 kg−1 in the grass-only control to 10.14 and 2.22 m3 kg−1 in alfalfa–grass mixtures, respectively. Interseeding alfalfa in wide rows had 23 and 26% less MC of revenue increment than interseeding in narrow rows, relative to grass only in Years 2 and 3, respectively (P <.01). Hay-type cultivars NuMex Bill Melton and WL 440HQ enhanced the forage mixture nutritive value more than the grazing-type Falcata–Rhizoma blend, mainly driven by greater alfalfa growth. Interseeding alfalfa into native grasses in wide rows can increase the efficiency of water use (lower WF) by enhancing forage nutritive value at low MC, thereby inducing a minimal trade-off in soil water consumption.