This thesis describes geological investigations for locating the new exploration well in the region of Spodnje Tinsko near the Žlof farm. During this work, I have cooperated with the Geo-Aqua Institute and the OKP Rogaška Slatina; the latter had the need for large quantities of quality drinking water in the region of Tinsko. After examining archival data and performing geological mapping I assessed that the area has good potential for providing additional quantities of groundwater, since mainly the Oligocene and Miocene clastic rocks and Quaternary sediments with subordinate occurences of Middle Triassic volcanics rocks are found in the surroundings of Tinsko region near Podčetrtek. Moreover, in the region of Rudnica Upper Triassic carbonates prevail which exhibit good permeability for the groundwater, and several boreholes already exist there for the abstraction of the drinking water. Subsequent research comprising (geophysical surveyings, drilling, and pumping test) has confirmed the hypothesis, as sufficient quantity of quality drinking water was provided with the new VT-4/15 well.