A weakly alkaline simple thermal spring of light mineralization (467.7 mg/kg dissolved solids), but with a generous 136.9 mg/kg of metasilicic acid that lands it squarely in Japan's beauty-water family — the silica leaves a thin film that makes skin feel noticeably smoother. At the wellhead the water shows a faint yellow tint with a slight metallic note in both taste and smell; the bath is fed from a storage tank rather than directly from the wellhead.
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⁺65.9mgP20 national66%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺15.2mgP32 national18%
- Magnesiummild; a laxative if you drink itMg²⁺4.9mgP50 national9%
- Potassiumminor; matters for drinking limitsK⁺6.5mgP38 national4%
- AmmoniumNH₄⁺1.7mgP77 national2%
- ManganeseMn²⁺0.30mgP53 national0.2%
- Iron (II)Fe²⁺0.20mgP39 national0.2%
- Iron (III)Fe³⁺0.20mgP66 national0.2%
- AluminumAl³⁺0.0000mg0.0%
- BariumBa²⁺0.0000mg0.0%
- CopperCu²⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻201mgP57 national78%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻30.4mgP23 national20%
- Hydrogen phosphateHPO₄²⁻2.7mgP91 national1%
- FluorideF⁻0.20mgP17 national0.2%
- SulfateSO₄²⁻0.70mgP6 national0.2%
- BromideBr⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- NitrateNO₃⁻0.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃137mgP66 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.50mgP8 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂131mgP83 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.