Accounting for the rigidity of water delivery systems ans spatial heterogeneity for the analysis of the impact of existing and potential water markets In response to the increasing water scarcity, water markets are sometimes proposed to reach an efficient allocation. Such markets already exist in a number of countries (USA, Mexico, India). However empirical studies analysing the impact of water markets are rare and not sufficient to recommend their implementation in other contexts, apart from a theoretical point of view. After a description of what is called water market the paper focuses on the literature analysing the economic impact of existing water markets. The impact of potential irrigation water markets in France and in Pakistan is then analysed using an economic model based on linear programming; this impact seems limited. However, the study identifies necessary physical and socio-economical conditions for such water markets to have a significant economic impact.