Aims: The trihalomethanes (THMs) concentration was investigated in some of rural water treatment plants in Khuzestan. Materials and Methods: Fifteen of the water treatment plants with the same drinking water source (Karoon river) were selected for analysis of THMs to assess the levels and the relationship between THMs and total organic carbon (TOC), pH, temperature, chlorination dose, and free chlorine residue. Results: THMs ranged from 1.8 to 219 mg/l in winter and 1.7 to 98 in summer, where the level in some treatment plants is higher than the Maximum Concentration Level (MCL). The ratio of total THMs levels was significantly correlated with temperature, pH, chlorination dose, and free chlorine residue, but negative correlation with TOC. Conclusion: Epidemiological studies using total THMs levels should be considered in the analysis of water treatment plant's results, and regulatory check of this parameter with drinking water guidelines.