The WaDI (water delivery for irrigation) model deals with the relations between the collective water supply and the demand within irrigated schemes. It is based on a separate modelling of the water supply and demand, including (i) a simplified representation of the hydraulic structure, characteristics and organizational parameters of the scheme, (ii) an assessment of the water demand of farms based on their total irrigated area, cropping pattern and irrigation practices, (iii) a farm typology, (iv) a confrontation between water demand and supply at each node of the scheme from pumping plants to tertiary canals, and (v) calculation of response factors between supply and demand during the peak demand period. "What-if" scenarios are simulated in order to enhance the stakeholders' capacity to plan strategic decisions such as water delivery allocation rules or infrastructure investments. WaDI was implemented on two Brazilian schemes. It allowed broadening the stakeholders' limited representation of collective water supply and demand into a more comprehensive understanding of these relations. The approach however showed some limits, along with the difficulty of assessing the real impact on the stakeholders' capacity for strategic planning.