There is a growing policy pressure to reduce water use in agriculture when this generates sufficiently large environmental benefits and increases the well-being of other water users. Several analysis investigate farmers’ response to water policy by means of mathematical programming models including Positive Mathematical Programming (PMP). The originals PMP methods refer only to activities observed in the reference period. However, under the pressure of new water policies, farmers can adjust not only their cropping patterns but also the irrigation techniques they use. In particular, they could introduce water deficit irrigation crop techniques that were not profitable in past conditions. This paper proposes an extension of the Röhm and Dabbert approach (2003) in order to include deficit irrigation crop techniques not observed in the reference period into a PMP model. These alternative techniques are identified by means of a crop growth model developed by FAO. The proposed methodology is applied to a Mediterranean area performing two sets of simulations considering : the increase of water cost and the reduction of water availability. The results shows that, when water availability decreases, not considering adjustments in irrigation techniques is likely to underestimate the extent of farmers’ response to the new policy scenarios. In facts, introducing deficit irrigation techniques can alleviate the negative impact of decreasing water availability on farm economic results by using more efficiently this resource. However, this is not the case for the considered water cost increases.