An objective methodology is proposed for assessing potential ground water yield on the basis of the randomness inherent in hydrogeological parameters as a result of uncertainty. Randomness is used here in the statistical sense to describe the ground water phenomenon on a regional basis. A systematic approach to selecting aquifer parameters is presented that leads to reliable ground water storage and subsurface flow estimates by incorporating a certain risk level. In addition, the averages of the specific ground water capacity and subsurface flow rate are calculated through a perturbation approach. This study demonstrates that cross-correlations between basic hydrogeologic variables might underestimate or overestimate model parameter values.