A sodium-led simple thermal spring, lightly mineralized at 158.8 mg/kg of dissolved solids and gentle on the body. Its alkaline pH of 9.18 gives the slippery, beauty-water feel that softens the skin, placing it among the more alkaline waters of its class. It is served at a retro Showa-era public bathhouse known for a painted Mt. Fuji mural.
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⁺50.0mgP13 national93%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.3mgP8 national5%
- PotassiumK⁺0.70mgP9 national0.9%
- AluminumAl³⁺0.20mgP65 national0.9%
- Iron (II)Fe²⁺0.20mgP38 national0.4%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻47.4mgP28 national32%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻20.4mgP67 national28%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻20.2mgP16 national23%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻15.1mgP28 national13%
- Fluoridetrace; drinking limits applyF⁻1.3mgP52 national3%
- HydroxideOH⁻0.30mgP74 national0.8%
- Hydrogen sulfideHS⁻0.40mgP50 national0.4%
- ThiosulfateS₂O₃²⁻0.20mgP53 national0.0%
- BromideBr⁻0.10mgP14 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃48.2mgP27 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.5mgP22 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.24mgP83 national
- CadmiumCd< —mg
- ChromiumCr< —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.