Chlorine is commonly used as a disinfectant in the drinking water treatment
process. However, chlorine may react with organic precursors such as humic
substances in water to form trihalomethanes (THMs). Since THMs are known c
arcinogens, their concentrations in water should be monitored. The aim of t
his research was to measure the concentrations of THMs in drinking water in
the 19 districts of Hong Kong. This study also reports, for the first time
, trihalomethanes-formation potential (THM-FP) of the drinking water in Hon
g Kong. While the THM-FP values measured are all below the WHO guideline va
lues, the total concentrations of THMs in tap water samples from 4 out of t
he 19 districts exceed the U.S. and U.K, standards. The measurements show t
otal THM levels of 104 mu g/L, 106 mu g/L, 115 mu g/L, and 131 mu g/L in Yu
en Long, Tsuen Wan, North, and Tai Po, respectively. Such high levels of or
ganic precursors could be an indication of the deteriorating state of the D
ongjiang River in Guangdong, where over 70% of Hong Kong's drinking water o
riginates. (C) 1999 Elsevier Science Ltd.