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In 2004, the World Health Organization proposed a new approach to risk assessment and risk management for drinking-water supplier, which is based on HACCP (Hazard Analysis and Critical Control Point) and termed “Water Safety Plans (WSPs)”. About four years later, Tokyo Waterworks developed WSPs in March 2008. In the WSPs of Tokyo Waterworks, control criteria are set for risk-related water quality items with general principle of using a 10 –50% value of the water quality standards, for the purpose of the early detection of the potential risk. On February 2008, a concentration of 1,4-dioxane exceeded the control criteria, which was set as 10% value (= 0.005mg/L) of the Japanese drinking-water quality standard (= 0.05mg/L). Removal of 1,4-dioxane in purification process is very difficult, so effective control measure of 1,4-dioxane is only by decreasing the concentration in raw water. However, the catchment management is outside the jurisdiction of the Tokyo Waterworks. This article represents a case study of the implementation of WSPs, focused on the efforts for protection raw water against 1,4-dioxane in Misato Purification Plant, which was selected as a model and started implementation since April 2007 precedent to other purification plant.

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