Impact of boiling on chemical and physical processes for reduction of halomethanes, haloacetonitriles, and haloacetic acids in drinking water

Tap water is boiled by families across the globe in their daily life for cooking food and beverages, as well as for controlling some chlorine-resistant organisms to improve the water quality. However, the effects of boiling methods (heating temperature, heating modes, open or closed containers) on water quality, in particular the reduction of disinfection byproducts (DBPs), are unclear. This comprehensive research demonstrates that during the heating process, trihalomethanes (THMs) were markedly decreased, haloacetonitriles (HANs) were drastically reduced and sometimes completely removed, while haloacetic acids (HAAs) were reduced the least. Heating to boiling in open containers reduced DBPs concentrations more than heating in the closed containers. Residual chlorine from 0.1 to 5.0 mg/L did not affect the removal of HANs, but could increase concentrations of HAAs likely due to reaction of organic matter with chlorine at elevated temperatures. THMs demonstrated good removal at 0.1-1 mg/L residual chlorine, but less removal at 5 mg/L residual chlorine. Sodium chloride (salt), often added as seasoning agent in the process of family cooking, was found to have little effect on the removal of DBPs during cooking and boiling. Compared with the toxicity of DBPs in tap water, boiling could greatly reduce both the cytotoxicity and carcinogenicity through removal of DBPs. Consequently, boiling of tap water had a significant effect on reducing human exposure to DBPs and their associated toxicities.