Water use in the Bardenas irrigation district The agro-environmental control of a basin such as the Ebro basin (Spain), comprising 800,000 ha of irrigation land, requires studies of hydrological irrigation sub-basins at a large scale of irrigation districts, in such a way that with a reasonable number of sub-basins, most of the irrigated area is controlled. This paper evaluates the water usage in the 59,200 ha of the Bardenas irrigation district, which belongs to the Arba basin (Zaragoza), as a pilot experience previous to the development of a control grid in the Ebro Irrigation lands. The methodology was based on the calculation of water balances (2004-2007) and the analysis of the irrigation quality indices proposed in the computational program Irrigation Land Environmental Evaluation Tool (In Spanish EMR 2.0). The study showed that 94% of the available water was used by crop evapotranspiration, although irrigation management was not adequate, generating an 8% hydric deficit. The average irrigation efficiency was 90%, reemphasizing the fact that the lower efficiencies at an Irrigation District level were related to higher drainage losses in surface irrigation (maximum irrigation drainage fractions of 28%) and to remarkable losses due to evaporation and wind drift of sprinkler irrigation (15% of irrigation supply). The water use index was high (84%), reaching a maximum value of 95% during drought periods. Thus, the improvement margin is limited, and therefore irrigation efficiency can be increased as well as the crop hydric stress can be reduced by: i) improvement of plot irrigation efficiency, ii) better regulation of surface runoff from both precipitation and irrigation return flows, to maximize reuse, iii) adaptation of sprinkler irrigation to lower temperature and wind hours, minimizing the evaporation and wind drift losses.