The source of water to wells is ultimately the location where the water flowing to a well enters the boundary surface of the ground-water system. In ground-water systems that receive most of their water from areal recharge, the location of the water entering the ground-water system is at the water table. The area contributing recharge to a discharging well is the surface area that defines the location of the water entering the ground-water system at the water table that flows to the well and is eventually discharged from the well. The calculation of areas contributing recharge to wells is complex because flow paths in ground-water systems change in response to development, and the aquifer material in ground-water systems is heterogeneous and is hidden from direct observation . Hypothetical experiments were undertaken to show the complexities in the delineation of areas contributing recharge to wells. Four different 'cases' are examined to demonstrate the effect of different conceptualized aquifer frameworks on deterministically calculated areas contributing recharge. The main conclusion drawn from the experiments is that, in order to understand the cause and effect relations that affect the quality of water derived from wells, the importance and nature of the variability in the ground-waterflow system must be considered and accounted for in any efforts to 'protect' the water supply.