Non point agrarian contamination makes its quantification and assignation to a specific territory difficult. The objectives of this work are to unify methodological criteria for agro-environmental evaluation and to propose indices to quantify irrigation-induced contamination. To this end, a computer programme called Irrigation Land Environmental Evaluation Tool (in Spanish EMR; http://acebo.pntic.mec.es/jcav0026/investigacion/EMR.htm) has been developed which evaluates the quality of irrigation and agro-environmental impact based on water, salt and nitrate balances in hydrological irrigation basins. The behaviour of the proposed indices is analysed using data registered in various irrigation districts in the Ebro valley (Spain). Salt and Nitrate Contamination Indices (SCI and NCI respectively) are based on the unitary mass of exported pollutants corrected by "natural and socioeconomic" conditions of irrigation districts evaluated. SCI and NCI are related to water and nitrogen use, key factors for minimizing contamination. SCI and NCI admit a greater mass of pollutants exported in the disadvantaged irrigation districts, which doesn?t prevent equally appropriate management being required in all irrigation districts evaluated. EMR is a user-friendly tool at the service of agro-environmental surveillance of irrigation land.