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It is essential to characterize the water use of plants that have potential for the stabilization of rising saline groundwater which could lead to increases in soil salinity. In this study, several techniques were used to determiiie the seasonal water use characteristics of the perennial grass Agropyron elongatum (tall wheatgrass) growing in a moderately saline, dryland environment with a fluctuating shallow groundwater tahle varying in electrical conductivity between 0 and 10 dS ni~'. Soil conditions were examined in terms of water potential measurements, plant water sources were identified using a stable isotope of water (deuterium, •^H) and evapotranspiration was estimated using hydrological and ventilated chamher methods. Seasonal changes in soil water potential were caused by salt accumulation and soil moisture leading to changes in plant water availability, particularly in the surface soil region over summer and autumn. Evapotranspiration in A. elongatum was high over summer during the peak period of growth (4 mm d~'), with evidence of water use from groundwater and from specific regions of the soil profile. Evapotranspiration was low during the period that A. elongatum was partially senescent in autumn (< 0-5 mm d~') and the lowest leaf water potential of-3 MPa that was measured occurred during this period of moderate water stress. Intermediate levels of water use (1-5 mm d~') were measured during winter when the entire soil profile was available for water uptake. Based on physiological characteristics, including aspects of summer water use, root morphology and salt tolerance in A. elougattun,, we conclude that this species is suitable for stabilizing the level of moderately saline groundwater in parts of southern Australia, which could reduce the potential for soil salinization.