Water resources become increasingly scarce, scarcity that will become acute in the coming years due, among others, to a reduction in water supply, as a result of climate change, and the increase in demand, accentuated by the population increase and the requirements of economic growth and development. In this context of scarcity, Morocco is confronted with the need to adapt its water management policy from a supply management to a demand management one. Implementing such a policy requires the adoption of new policy instruments and decision making support tools that take into account the complexity of the current and future situation, as well as allowing the assessment of the economic, social and environmental impacts of various water resources allocation alternatives at the overall river basin level. This paper compares several methods for calculating the water value and proposes an integrated economic water management model at the river basin scale. This model takes into account the economic, institutional, hydrological and agricultural aspects, as well as the behavior of various agents involved in water resources management and the competition among sectors. One Major contribution of this model is a detailed disaggregation by spatial units (hydrological units, cropping areas, and grazing land), by agricultural production systems (irrigated and rainfed crops), and by farm sizes. Basically it’s an optimization model with a non linear objective function, and using the positive mathematical programming method technique for its calibration. Given the conjunctive use of water at the river basin level, the model results show the tremendous impact of surface water management on the overexploitation of the ground water and the risk of its depletion. A management policy of surface water based on administrative pricing, pumping cost, and water supply marginal cost is proven inadequate for a sustainable resource management since it underestimates the overall water scarcity at the river basin level.