In this age of computers, numerical models are being extensively used in analysing groundwater flow problems. Over the last ten years geologists and hydrologists have developed a range of groundwater simulation programmes which model aquifer behaviour and displacement. Models have been developed for un-confined, semi-confined and confined aquifers and combinations of these, enabling planners to evaluate aquifer performance, re-charge and dis-charge. These models cannot be so easily applied to multi-aquifer systems nor to those with unsaturated flow.