By law, the overdrafting of groundwater in the Phoenix, Arizona, area must cease by the year 2025. Safe yield can be achieved by means of conservation, water supply augmentation, and condemnation of groundwater pumping rights. With 40% of water supply coming from groundwater, achievement of safe yield will mean dramatic changes to groundwater users - especially to irrigated agriculture, the billion dollar sector of the economy which uses up to 70% of this water. A regional approach is adopted to specify aquifer parameters and water production costs to enable an economic analysis of the effects of groundwater pumping reductions on the agricultural sector to be made. The assumptions and application of this methodology are explained, and the direction of continuing research is detailed.