Ordinarily Legionella is sterilized with chloride germicide for the bath water in the recirculation and purification system. The germicide, however, changes chemical properties of hot spring water or bath liquid. So we designed a heat-recovery heating sterilization system and evaluated its sterilization and energy saving performance using an experimental facility which mechanically circulates and purifies the bath water. Through a long-term experiment, it was shown that no Legionella was detected in supply water to a bathtub after retained in a tank at 77 degrees C for more than two minutes and that the sterilization system could be operated with approximate one tenth of heating energy which is consumed to heat the water up to the same temperature without heat recovery.
