Trihalomethanes formation in Iranian water supply systems: predicting and modeling. 
Trihalomethanes (THMs) were the first disinfection by-products discovered in drinking water and are classified as probable carcinogens.  This study measures and models THMs formation at two drinking water distribution systems (WDS1 and WDS2) in Ahvaz City, Iran.  The investigation was based on field-scale investigations and an intensive 36-week sampling program, from January to September 2011.  The results showed total THM concentrations in the range 17.4-174.8 μg/L and 18.9-99.5 μg/L in WDS1 and WDS2, respectively.  Except in a few cases, the THM concentrations in WDS1 and WDS2 were lower than the maximum contaminant level values.  Using two-tailed Pearson correlation test, the water temperature, dissolved organic carbon, UV254, bromide ion (Br-), free residual chlorine, and chlorine dose were identified as the significant parameters for THMs formation in WDS2.  Water temperature was the only significant parameter for THMs formation in WDS1.  Based on the correlation results, a predictive model for THMs formation was developed using a multiple regression approach.  A multiple linear regression model showed the best fit according to the coefficients of determination (R2) obtained for WDS1 (R2=0.47) and WDS2 (R2=0.54).  Further correlation studies and analysis focusing on THMs formation are necessary to assess THMs concentration using the predictive models.