Classified as an alkaline simple weak-radon spring — a gentle, lightly mineralized water of the simple-thermal type. With dissolved solids of only 140 mg/kg it sits at the light end of the scale and feels soft on the skin. Being alkaline, it carries the slippery touch of Japan's beauty-water family, even though its mineral content is modest.
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⁺36.0mgP8 national90%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.1mgP12 national9%
- Potassiumminor; matters for drinking limitsK⁺0.60mgP7 national1%
- Aluminumshows up in acidic volcanic waterAl³⁺0.10mgP37 national
- LithiumLi⁺0.07mgP18 national
- StrontiumSr²⁺0.01mgP10 national
- Manganesetrace; companion to iron springsMn²⁺0.0010mgP14 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻40.9mgP24 national41%
- Fluoridetrace; drinking limits applyF⁻9.0mgP89 national28%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻8.1mgP11 national14%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻1.9mgP24 national10%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻8.1mgP19 national7%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃21.9mgP6 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.9mgP17 national
- ArsenicAsNDmg
- LeadPbNDmg
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.