Greening the economy is mostly about improving water governance and not only about putting the existing resource saving technical alternatives into practice. Focusing in the second and forgetting the first risks finishing with a highly efficient use of water services at the level of each individual user but demanding an unsustainable amount of water for the entire economy. This might be happening already in many places with the so-called modernization of irrigated agriculture: the world’s largest water user and the one offering the more promising water saving opportunities. Actual savings seem to be far from expected and modern irrigation techniques seem not to be contributing to reduce water scarcity and increase drought resilience. In fact, according to the little evidence available, they seem to be doing the opposite: increasing water demand and depletion. Building on basic economic principles this paper aims at showing the conditions under which this apparently paradoxical outcome might appear. This basic model is expected to serve as guidance for assessing the actual outcomes of enhancing irrigation efficiency and to discuss the changes in water governance that would be required for this to make a real contribution to a sustainable water management.