THMs in Re-Chlorinated Drinking Water

The concentration of trihalomethanes (THMs) could increase significantly in post-chlorinated water especially as water is boiled. This study aimed to investigate the levels of THMs and residual chlorine in the existing water distribution system, and to evaluate the possibility of additional THMs formation in distribution system for drinking water and re- chlorinated drinking water in roof water tank. The investigation results showed that the level of residual chlorine in main pipelines generally lies between 0.5 and 1.2 mg l^-1, decreasing to less than 0.4 mg l^-1 or even close to zero (not detectable) at the end of pipelines. The level of total THMs in both main pipelines and the end of pipelines was found to lie between 11.4 and 16.3 mug l^-1. However, a significant increase in THMs level was observed in post-chlorinated water, especially when water is heated.