A strongly alkaline simple thermal spring at pH 9.9. With only about 168 mg/kg of dissolved solids it is lightly mineralized and gentle on the body, while the high alkalinity gives the pronounced slippery feel of Japan's beauty-water family. At the source the water shows a faintly pale-yellow, slightly turbid look with a weak sulfur note.
Good for
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺48.8mgP13 national96%
- StrontiumSr²⁺1.5mgP82 national3%
- HSiO3HSiO₃⁻66.8mgP96 national39%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻—mg20%
- Fluoridetrace; drinking limits applyF⁻17.2mgP98 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.