The aim of this study is to measure the radon ((222)Rn) concentrations in drinking water and river water in the region of Tokat city in Turkey. The measurements were performed by analysing the water samples collected from tap water, spring water and Yesilırmak river water flowing through the centre of the city of Tokat. The obtained radon concentrations ranged from 0.48 ± 0.22 to 1.30 ± 0.27 Bq l(-1) in tap water, from 0.13 ± 0.17 to 1.20 ± 0.29 Bq l(-1) in spring water and from 0.09 ± 0.12 to 0.83 ± 0.17 Bq l(-1) in the Yesilirmak river water. The results are presented and compared with other studies. From these data, the average effective dose equivalent from radon in tap water and in spring water has been estimated as 5.0 and 3.0 µSv y(-1), respectively.