Is advanced treated water truly high quality?: the answer from a viewpoint of cancer risk induced by trihalomethane class.

Before and after switching to the advanced treatment, a total of 48 trihalomethanes measurements was made at household taps in the specific distribution area in Osaka City, Japan. An average of total trihalomethanes concentrations in advanced treated water was three-fifths of that in conventionally treated water. The average lifetime cancer risks for total trihalomethanes were 48.5 × 10(-6) in conventionally treated water and 44.8 × 10(-6) in advanced treated water, which were higher than 10(-6), the negligible risk level. Surprisingly, the average lifetime cancer risk of conventionally treated water was not significantly different from that of advanced treated water. The highest value of hazard index found was an order of magnitude lower than unity.