Since 1972, the Kanamachi Purification Plant has been faced with a “musty odor” problem in water. In 1984, the plant began to treat raw water with powdered activated carbon. However, the concentration of the musty odor substance 2-methylisoborneol (MIB) in raw water varied so markedly that it was difficult to control the dosage of powdered activated carbon. To achieve a more stable and effective removal of the musty odor, the Bureau decided to introduce an Advanced Water Purification system combining ozonation and biological activated carbon (BAC) treatment. On June 25, 1992, we started operation of the facilities. This system, which is the first of these plants in Japan, can remove musty odor to the satisfaction of the customer.