The purpose of this research is to quantify how macro-scale factors such as weather, crop prices, and land conversion affect agricultural water use at the irrigation district level in central Arizona and to understand what constraints and considerations district managers face when making water-sourcing decisions. A conceptual model is developed and econometrically estimated finding that much of the annual variation in total water use for agriculture can be explained by differences in precipitation, cotton prices, and alfalfa prices. Further, results from empirical analysis support the notion that total water use for agriculture has been greatly affected by land conversion from agriculture to other uses. Irrigation district manager interviews indicate that the water sourcing process is very similar across districts in central Arizona and has varied little since 1995, due to common constraints. This research lays an important foundation for future models designed to forecast agricultural water use in central Arizona.