The water at onsen (hot spring) facility Happo no Yu’s open-air bath is very special indeed. A study by the Nippon Onsen Research Institute revealed that the spring has a significantly elevated level of hydrogen concentration. Drinking or bathing in this hydrogen-rich onsen water is said to achieve anti-aging effects.
*You will experience peak hydrogen concentration five minutes after entering the bath: the ppb (parts per billion) you will encounter is 50–60, although at the hot spring’s tap that rises to an amazing 120 ppb.