2020 Volume 89 Issue 9 Pages 12-23
Trihalomethane is formed in drinking water primarily as a result of chlorination in water supplies. The extent of trihalomethane formation fluctuates in a variety of situations. The level of trihalomethane can get higher with increasing residence time in water supply systems and in households. Furthermore, heating of water at the point of use increases the concentration of trihalomethane dramatically. Trihalomethane is regulated only in the water which has just come out of taps, prior to any household treatment (heating, filtering, etc.). Therefore, many water suppliers control their water quality according to regulations. However, there is a need to consider the fate of water when controlling water quality. A new method is necessary to evaluate the trihalomethane maximum potential in the water for better management of water quality. In this study, we developed a method for estimating the trihalomethane maximum concentration (THMmax) by heating water in PFA bottles. The THMmax was the total concentration of trihalomethanes (chloroform, dibromochloromethane, bromodichloromethane, and bromoform) after heating at 80°C for 10 hours. The THMmax was suitable for evaluation because it was stable and independent of either residence time or water temperature. We conducted monthly monitoring of the THMmax at Nagasawa water purification plant in Kawasaki city. The average of the THMmax was 49μμ/L, which was 8.3 times as much as that of the total trihalomethanes (5.9μμ/L) in unheated water. The trends showed that compared to trihalomethane in unheated water, the THMmax changed less throughout the year and did not decrease so much in winter.
