It is postulated that water resource needs are importantly affected by both size and composition of population dispersion, and that migration patterns are the major sources of uncertainity in predicting population change. A predictive model for migration behavior was studied. Using principally multiple regression analysis on migration across state economic area boundaries in the form of out-migration rates for 1949-50, it is concluded that migration rates are a dynamic phenomonon dependent primarily on accessibility (transportation, communication, information, distance) and available opportunity (employment rates, income, amenities). However where accessibility is low (e.g., poor communication, great distance) out-migration is not significantly affected by differential opportunity. A strong case is made for better statistical data.