This paper analyzes the effects of some water management policies and irrigation systems on crop yields and water pollution, in an area located in the Flumen- Monegros irrigation district in Huesca (Spain). The analysis is performed using water and nitrogen crop response functions, which are estimated with the EPIC crop growth package. The estimation of response for the crop activities incorporates information on local climate, soils, crop management and irrigation systems. The relationship between yields and water and nitrogen input use is examined, in order to quantify the pollution reduction cost faced by farmers. The costs depend on the particular crop and the pollution abatement measure, and information on these costs is important to design efficient pollution abatement measures.