Background: It is considered that if radon gas is inhaled and ingested, it is the primary health risks for lung and stomach cancers. This paper presents the measurement results of radon activity concentrations both residential tap water and dam water for Kastamonu city Centre-Turkey. Materials and Methods: The radon activity concentrations of water samples collected from 60 tap waters at four locations and 12 dam water of study area were determined. Radon concentrations were measured using the professional radon monitor AlphaGUARD PQ2000 PRO (Genitron Instruments). Results: The mean value for all residential tap water samples and dam water samples were ascertained as 0.050 Bq l^-1 and 0.741 Bq l^-1, respectively. The annual effective doses were calculated for the inhalation of radon released to air when water is used and the ingestion of drinking water. The mean values for inhalation and ingestion were found to be 0.1266 μSv y^-1 and 0.0105 μSv y^-1, respectively. For the radon exposure from ingestion, the annual effective doses were calculated for infants, children, and adults, separately. Conclusion: When the results compared with the internationally recommended safe limits, the tap waters of Kastamonu city Centre is safe for drinking purposes in terms of radon activity concentrations.