ABSTRACT: The change in geothermal water exploitation (replacing of the free outflow by increased pumping) could cause changes in geothermal water properties not only in a respective geothermal well, but consequently, in the whole geothermal structure. As an example of such changes, geothermal well VZO-13 Zlatna na Ostrove (Slovakia) was chosen. Qualitative properties of geothermal water exploited by free outflow of 7.5 l.s-1 were compared with those, exploited by pumping with the rate of 18.33 l.s-1. The value of TDS has increased from 2.5 g.l-1 to 13 g.l-1. The change was accompanied by changes of gas composition and content. The total gas content increased from 274 l.m-3 to 1 117 l.m-3, nitrogen content decreased from 20 l.m-3 to 1.8 l.m-3, CO2 content increased from 15 l.m-3 to 57 l.m-3 and the methane content increased from 239 l.m-3 to 1 058 l.m-3. The change in gas content resulted in the change of bubble point depth which decreased from 150 m (by the free outflow of 7.5 l.s-1) to the depth of 250 m below the surface (by the pumping rate of 18.33 l.s-1). Hydrodynamic calculations also documented that by the long-term abstraction of the 18 l.s-1, the free outflow will disappear and the piezometric head of geothermal water will decrease to the depth of 85 m below the surface.