An alkaline simple thermal spring led by sodium and calcium with a touch of sulfate and chloride. At pH 8.8 it sits firmly in Japan's beauty-water family, with the slippery, skin-smoothing feel that comes from the alkaline-bicarbonate side of the spectrum. Lightly mineralized at 371.9 mg/kg dissolved solids — a gentle, low-irritation soak. The 31.7 °C source is reheated for bathing as a cold-low spring.
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⁺64.2mgP19 national53%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺48.6mgP57 national46%
- MagnesiumMg²⁺0.50mgP20 national0.8%
- PotassiumK⁺0.60mgP7 national0.4%
- AluminumAl³⁺0.0000mg0.0%
- BariumBa²⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻133mgP59 national55%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻60.9mgP31 national34%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻22.3mgP14 national7%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻5.4mgP36 national4%
- FluorideF⁻0.30mgP24 national0.4%
- HydroxideOH⁻0.10mgP50 national0.2%
- BromideBr⁻0.20mgP30 national0.0%
- AsO2AsO₂⁻0.0000mg0.0%
- BO2BO₂⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃32.9mgP15 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.4mgP22 national
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CopperCu0.0090mgP58 national
- CadmiumCd0.0030mgP79 national
- ArsenicAs< —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.