In order to determine the natural radionuclides in portable water, samples were collected from fifty locations in Northern part of Kaduna state and were subjected to the investigation of the presence of naturally occurring radionuclides. The radionuclides investigated are potassium-40, uranium-238 and thorium-232 using sodium iodide detector (NaI (Ti)). Results showed that potassium-40 concentration in the water samples has minimum and maximum concentration as 0.124 and 0.849 Bq/L, respectively. The mean value of potassium-40 concentration found in water is 0.416 Bq/L. Also, uranium-238 and thorium-232 investigated in the samples gave mean concentration of 0.0011 and 0.00006 Bq/L, respectively. The results obtained from these analysis shows that samples have radionuclides activity concentration below the recommended value for the radionuclides.

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A total forty two (42) sampled points were investigated for radioactivity level and health implication using standard method. The exposure dose rate  ranged from 14 to 32μRh-1 with an average value of μ23Rh-1. Dose rate and equivalent dose rate ranged from 121.8 to 278.4nGyh-1 and 1.18 to 2.69mSvy-1 respectively. The average value of the indoor annual effective dose equivalent (AEDE), outdoor AEDE, and excess lifetime cancer risk (ELCR) were computed to be 0.936 mSvy-1, 0.311 mSvy-1 and 0.810 x 10-3 respectively. Analysis of dose to human organs; testes and ovaries, were 0.61 and 0.43 mSvy-1 respectively. Exposure rate, dose rate and ELCR exceeded the recommended values. All the outdoor AEDEs were within the permissible value of 1.0 mSvy-1 for general public and below the limit of 20 mSvy-1 for radiological workers as recommended by InternationalCommission on Radiation Protection (ICRP). Keywords: Assessment, Environmental radioactivity, Exposure dose, Health impact