Liquidation works carried out since 1994 in the post exploitation workings of the sulphur mine Machow are nearing completion. Its expected that by the end of the year 2000 the horizontal isolation layer forming the base of the future water reservoir will be completed. Dewatering of the mine however has to be continued at least until the partial filling of the reservoir by waters from the Wisla. At that time the pressure of the ore waters of the tertiary layer will be in equilibrium within the recreational reservoir which won't cause the breakup (disintegration) of the newly formed isolation layer. In the end phase of its functioning the dewatering barrier system will undergo continual changes. These will occur as a result of the necessity of moving the internal well barrier from the base of the ore or the above-ore layer to the perimeter of the future water reservoir (external barriers). The quantity of withdrawn ore waters will ensure the maintenance of the hydraulic height in the vicinity of the liquidated mine. The change in water relations was prognosed using a hydrogeological model of the Tarnobrzeg sulphur depression, this allowed a piezometric estimation of the effectiveness of the ore dewatering system (Table 2) during consequent phases of the liquidation process. Each of these phases is also documented in the form of hydroizohip maps (fig. 1-4) presenting the expected position of the hydrodynamic fields. These maps also show the increase in water table heights (impression) as compared to the state at the end of 1999 which is accepted as the initial state in simulation calculations. The obtained results from the prognostic calculations form the basis for the design or modification of barrier wells. During the filling up period of the reservior they will be helpful in a rational water management scheme.