The resultsof 222Rn and 226Ra activity measurements in drinkable water supplies of theThu Duc region in HoChiMinh City,Vietnam,arep resented in this paper.The measurements wereper formed using a
RAD 7 radon detector manufactured by Durridge Company,Inc.Mean concentrations of 222Rn and 226Ra
were found to be 0.117 0.01Bql1 and 0.117 0.02 Bql1 in 14 drinking water samples.Theyare
0.127 0.01Bql1 and 0.107 0.02 Bql1 in 15 tap water samples,respectively.Themean 222Rn con-
centration of 1.407 0.03 Bql1 in the 20 groundwater samples of this study is also lower than the WHO advised levelof100Bql1. Fiftypercentofgroundwatersamplesanalysedhave 226Ra levelsinexcessof
the USEPA recommended maximum contaminant level of 0.185 Bql1. The occurrence of elevated
concentrations of 226Ra in groundwater samples was explained by pH and alkaline conditions