[en] The use of depleted uranium ammunition in South Serbia during the 1999 Kosovo conflict raised a great deal of public concern in the Balkans. Radioactivity levels of ²³⁸U in 20 wells and lake water samples were checked from the viewpoint of internal radiation exposure for South Serbian subjects. We have measured ²³⁸U concentration using inductively coupled plasma mass spectrometry, whereas thermal ionisation mass spectrometry has been used for the measurement of isotope ratios, e.g. ²³⁴U/²³⁸U and ²³⁵U/²³⁸U. The concentration of uranium in water samples varies in the range 1.37-63.18 mBq/L. ²³⁴U belongs to the ²³⁸U natural radioactive decay series, and at secular equilibrium, the abundance ratio, ²³⁴U/²³⁸U, corresponds to the ratio of their half-lives. The ²³⁴U/²³⁸U activity ratio varies in the range 0.88-2.2 and ²³⁵U/²³⁸U isotope ratio varies from 0.00698 to 0.00745. These findings indicate that uranium in water was a mixture of natural and anthropogenic origin. The annual effective dose due to ²³⁸U was estimated to be in the range 9.2 x 10^-5 - 2.1 x 10^-3 mSv. (authors)