The level of radon concentration has been assessed using the Advanced SMART RnDuo technique in 30 drinking water samples from Jammu district, Jammu and Kashmir, India. The water samples were collected from wells, hand pumps, submersible pumps, and stored waters. The randomly obtained 14 values of radon concentration in water sources using the SMART RnDuo technique have been compared and cross checked by a RAD7 device. A good positive correlation (R2 = 0.88) has been observed between the two techniques. The overall value of radon concentration in various water sources has ranged from 2.45 to 18.43 Bq L−1, with a mean value of 8.24 ± 4.04 Bq L−1, and it agreed well with the recommended limit suggested by the European Commission and UNSCEAR. However, the higher activity of mean radon concentration was found in groundwater drawn from well, hand and submersible pumps as compared to stored water. The total annual effective dose due to radon inhalation and ingestion ranged from 6.69 to 50.31 μSv y−1 with a mean value of 22.48 ± 11.03 μSv y−1. The total annual effective dose was found to lie within the safe limit (100 μSv y−1) suggested by WHO. Heavy metal analysis was also carried out in various water sources by using an atomic absorption spectrophotometer (AAS), and the highest value of heavy metals was found mostly in groundwater samples. The obtained results were compared with Indian and International organizations like WHO and the EU Council. Among all the samples, the elemental analysis is not on the exceeding side of the permissible limit.