The occurrence of 51 volatile organics in water supplies at nine municipalities along the Great Lakes and for a well water supply was examined by a GC-MS technique. Only dichloromethane (max. 19.0#x3BC;g/L) and chloroform (17.0#x3BC;g/L) were detected at concentrations above 10.0 #x3BC;g/L and bromodichloromethane, chlorodibromomethane, dichloroacetonitrile, toluene, and styrene were detected at least once above 10.0#x3BC;g/L. Aggregate levels of the 19 organics detected at #x2265; 0.1 #x3BC;g/L were generally about the same in treated and raw water when values for trihalomethanes (THM) and dichloroacetonitrile were excluded. THM values did not exceed 32#x3BC;g/L. The aggregate frequency and the mean of aggregate organics levels were noticeably lower for raw water in winter than in summer or spring. Overall, the water treatment at the sites was not very effective in removal of relatively low levels (0.1 to 5 #x3BC;g/L) for the volatile organics from raw water. There were no evident trends to the occurrence of organics along the Great Lakes system. Levels of organics in raw and treated water were generally about the same as, or lower than, those previously found in other Canadian surveys.
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