A bicarbonate spring led by sodium, calcium and magnesium — neutral pH, hypotonic, moderately mineralized. The wellhead carries a tangible carbonated taste with a faint astringent edge, hinting at the spring's freshness. A generous 201.5 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother, placing it in the Japanese 'beauty-water' family.
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⁺147mgP39 national38%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺99.3mgP73 national29%
- Magnesiummild; a laxative if you drink itMg²⁺56.3mgP86 national27%
- Potassiumminor; matters for drinking limitsK⁺26.2mgP71 national4%
- Iron (II)Fe²⁺2.3mgP74 national0.5%
- LithiumLi⁺0.50mgP55 national0.4%
- AmmoniumNH₄⁺1.1mgP67 national0.4%
- StrontiumSr²⁺0.40mgP62 national0.1%
- ManganeseMn²⁺0.20mgP45 national0.1%
- BariumBa²⁺0.10mgP53 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻773mgP85 national74%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻93.4mgP39 national15%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻86.7mgP52 national11%
- FluorideF⁻0.20mgP17 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃202mgP86 national
- Metaboric acidHBO₂15.8mgP69 national
- Metaarsenious acidHAsO₂0.10mgP56 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂537mgP96 national
- 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.