Extreme weather conditions have caused difficulties in the Hungarian drinking water management many times in the past. High demand for drinking water in dry summer periods and the accompanying reduction in water resources lead to insufficiency in the availability of a number of water supplies, therefore causing limitations in water access. In some other cases, as a result of excessive precipitation, floods and flash floods evolved over karstic areas, and several water supplies had to be excluded from operation in order to avoid the risk of infections. The expected increase in the number of extreme weather conditions and further possible changes in future climate necessitates the analysis of the vulnerability of drinking water resources to climate change. Since 95% of the total drinking water supply in Hungary originates from subsurface layers, significance of groundwater resources is outstanding. Our work was carried out in the frames of the NAGiS (National Adaptation Geo-information System) project with the aim to devise a methodology for the study and determination of the vulnerability of drinking water supplies to climate. Methods have been chosen according to the CIVAS (Climate Impact and Vulnerability Assessment Scheme) model that has been developed in the frame of the international climate research project CLAVIER (Climate Change and Variability: Impact on Central and Eastern Europe). The CIVAS model, being based on the combined evaluation of exposure, sensitivity, impact, adaptability, and vulnerability provides a unified methodical scheme to quantitative climatic impact assessment. The investigation involves the analyses of climatic parameters primarily influencing drinking water supplies and hydrogeological characteristics of the geological media that significantly determines vulnerability. Apart from the expected environmental changes,societal and economic processes have also been taken into account. Climate vulnerability has been determined on the basis of the distribution and categorization of the chosen indicators. Further effects, independent of climate change and caused by anthropogenic activity, result in similar phenomena. It is often difficult to differentiate between natural and anthropogenic effects that occur simultaneously; therefore, anthropogenic activity is necessary to be taken into account. In the analyses we used data of two different climate models covering two separate future time periods. Results on the basis of both climate model projections suggest that a considerable number of regions in the area under investigation appear to be vulnerable to climate change to a certain extent, and vulnerability intensifies to the end of the 21st century.