The aim of this study was to determine natural radioactive and heavy element concentrations in Mersin drinking water samples before the commissioning of the Akkuyu nuclear power plant and to collect data for possible environmental contaminations in the future. Drinking water samples were taken from the provincial center, districts, and populated villages. The annual effective dose of natural radionuclides and cancer risks were calculated for each person living in the city. Hazard index and cancer risk were calculated, which were caused by heavy elements. Mean gross alpha and beta radioactivity concentrations in drinking water were 0.059 Bq/L and 0.120 Bq/L, respectively. The annual cumulative effective dose for people was 30.83 $\mu $Sv. Average estimated excess cancer risk related to this exposure was 16.9 $\times $ 10$^{-5}$. Mean metal concentrations of Cr, Ni, Zn, Cu, Ba, and Cd in drinking water were 1.33, 4.65, 54.8, 11.1, 26.3, and 0.36 $\mu $g/L, respectively. Pb and As were lower than the detection limits. Mean calculated hazard index depending on heavy metal concentration was 6.8 $\times $ 10$^{-1}$ for drinking water. Cancer risks of heavy metals decreased in the order of Cd $>$ Cr $>$ Ni for the region.