The North West Province is located on latitude 25.8˚S and longitude 25.5˚E and offers an almost year-round sunshine, with average rainfall of 300 - 500 mm annually. This study was carried out within the Mafikeng Local Municipality (MLM), the biggest municipality in the Province which covers an area of about 3703 km² and consists of 102 villages and suburbs. Economic activities within the municipality consist of agriculture, agro-industries and tertiary sectors.

The concentration of heavy metals in the water samples was determined using the Inductive Coupled Plasma Mass Spectrometer (Perkin Elmer NexION 300Q) located at the Animal Health Centre of the North West University, Mafikeng Campus. Prior to analysis, samples were digested as described by [5] with modifications. To 5 ml aliquot of samples, 5 ml of 55% HNO₃, 5 ml of 32% HCl and 1 ml of 100 vol. H₂O₂ were added, followed by heating in a microwave for 45 min. The mixture was allowed to cool for 20 min and later transferred to pre-rinsed 100 ml volumetric flask where it was topped with distilled water to make 100 ml. The mixture was left at room temperature overnight and thereafter transferred to 15 ml centrifuge tubes without disturbing the sediments.

Determination of gross alpha/beta activities in water samples was carried out by Liquid Scintillation Counting (LSC) using the Perkin Elmer Quantulus 1220 Ultra-Low Level LSC coupled to alpha-beta discrimination (Todorović et al., 2012). A 10 ml aliquot of each filtered and acid-preserved water sample was added to 8 ml of Ultima Gold ULLT Cocktail (Perkin Elmer, Boston, USA) in a 20 ml vial. The water samples were then run on the Quantulus 1220 Ultra Low-Level LSC set at 4 h counting time, 3 cycles and 1 repetition per sample vial. The radionuclide concentrations in samples were determined using HPGe detector model GC2020 E7500 CSL (Canberra GMbH) {resolution (FWHM) at 122 keV (⁵⁷Co) is 0.94 keV and at 1332 keV (⁶⁰Co) is 1.77 keV and relative efficiency for energy 1.33 MeV relative to (NaI)TI is 20%. The detector was coupled to a computer through an MCA (DSA 1000, Canberra). The detector was calibrated for energy and efficiency using the Canberra standard calibration file. Each sample was counted for 24 h. The Genie 2000 software was used for both Data acquisition and analysis (nuclide identification).

The annual intake dose (AID) of some important radionuclides through drinking water over one year period for all age groups was calculated for community water using the following equation [6]

where I is annual water consumption (L/a), A is the activity concentration (Bq/L) and C is the dose conversion factor for each radionuclide. The dose conversion factors and annual water consumption (L/a) for different age groups was extracted from DWAF (2002) guidelines [7] . The total annual dose was calculated as the arithmetic summation of annual intake dose of two radionuclides (²³⁵U and ²²⁶Ra).

The heavy metal concentration of analyzed water samples is shown in Table 1. The values of all the metals detected in samples obtained from the Mafikeng WWTW were within limits stipulated by the Department of Water Affairs (DWA) and World health Organization (WHO) although there were staggering variations in values at different processing stages. This could be due to effects of treatment. However, most of the metals were not detected in the water out samples (i.e. effluents released to the Setumo dam) except vanadium, iron and arsenic which were also far below stipulated limits. This observation is a suggestion that the water treatment carried out at the WWTW may be very efficient in removing the heavy metal contents of the wastewater delivered to it.

The gross α/β activities in water samples as determined by liquid scintillation counting are presented in Table 2. The gross β activity concentration of water delivered to the treatment plant was within limits of both South Africa Target Water Quality Range (SA-TWQR) and WHO. The activity was not detected at the two treatment stages and the effluent released from the treatment plant. In contrast, the gross α activity concentration of samples highly exceeded the limits set by WHO for water. The gross α concentration in water sample from first treatment stage was higher than that of the waste water delivered to the plant although there were little but steady decreases in the second treatment stage and the effluent. Perhaps the first stage of the water treatment involved the use of chemicals/substances that contain alpha-emitting particles which invariably must have increased the gross alpha concentration of the water. The treatment applied in the second stage however, seemed not to have been efficient in removing the alpha emitters hence the high concentration in the effluent. It has been noted that gross alpha activity, in particular, is a sensitive and immediate indicator of the concentrations of uranium isotopes (²³⁴U, ²³⁵U and ²³⁸U) and ²²⁶Ra in water [10] . Because of the high radiotoxicity of these common α-emitters, the gross α concentration recorded in the current study calls for concern and further evaluation of the individual radionuclide activity concentration for the purpose of risk assessment. This is in view of the fact that the effluent from the treatment plant drains into the Setumo dam where water for domestic use is abstracted.

The trend observed in the concentrations of both Uranium-235 and Radium-226 radionuclides from waste water entering the treatment plant (²³⁵U = 9.75 Bq/L and ²²⁶Ra = 5.44 Bq/L) to the effluent (²³⁵U = 16 Bq/L and ²²⁶Ra = 5.56 Bq/L) in Table 3 may be an indication of poor efficiency of the employed water treatment method in removing the radionuclides. This could cause the respective radionuclides which naturally have long half-lives (²³⁵U = 700 million and ²²⁶Ra = 1600 years) to accumulate in the system over time leading to further contamination of water during processing. Furthermore, it was previously noted that effluents delivered into the Setumo dam (source of water for domestic use) are of poor quality, and which eventually reduces the efficiency of the final water treatment at Mmbatho water treatment plant [11] . This could be a contributing factor to the exceedingly high concentrations of the radionuclides in the community water (²³⁵U = 73.8 Bq/L and ²²⁶Ra = 47 Bq/L). This is in addition to probable contamination of the community water delivery system as a result of previous radionuclide accumulations, which in turn may contaminate the delivered water. It has been reported that most water treatment methods generate waste products containing concentrated radionuclides which if not properly handled or treated, become a source of radiation in itself [12] . However, the studies of [3] in South India showed that water treatment by reverse osmosis reduced the concentrations of natural radionuclides in drinking water. The high activity concentration of uranium and radium nuclides observed in this study agrees with reports of [13] , who also noted high dose contributions of radium (48.0% ± 27.9%) and uranium (20.3% ± 14.1%) in drinking water in Italy. Evaluation of activity concentration of ²²⁶Ra in drinking waters from oil fields and host communities in Nigeria revealed average concentration that was well above the WHO permissible levels [6] . Uranium and radium are natural radionuclides of practical importance in terms of drinking water due to their effects on health. Radium tends to accumulate in the bony skeleton leading to increased risk of bone cancer particularly when the activity concentration is above 0.42 Bq/L. Uranium has affinity for kidneys and liver making its chemical toxicity to be of greater concern than the radiological cancer risk. Short term risk of renal damage may occur with activity concentration of uranium greater than 18 Bq/L of drinking water [8] . The estimated annual intake dose and the total annual radiation dose (μSv∙yr⁻¹) resulting from consumption of ²³⁵U and ²²⁶Ra in drinking water are presented in Table 4.

Despite the high activity concentrations of the two natural radionuclides in the community water, the estimated total doses for the analyzed water samples were all well below the reference level of the committed