A sodium bicarbonate cold mineral spring of the classic juso-sen style: alkaline at pH 8.6-8.8, soft on the skin, and squarely in Japan's beauty-water family. Metasilicic acid at 63.9 mg/kg reinforces that smooth, faintly slippery feel. The certificate also logs 30.0 mg/kg of humic matter, and the wellhead sensory reading describes the water as blackish yellow with a faint iron taste. At 20.9 °C it is a cold mineral spring (below 25 °C), so it is heated for bathing.
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⁺272mgP60 national93%
- Potassiumminor; matters for drinking limitsK⁺12.5mgP49 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.5mgP18 national2%
- Magnesiummild; a laxative if you drink itMg²⁺3.1mgP40 national2%
- AluminumAl³⁺0.50mgP75 national0.5%
- Iron (II)Fe²⁺1.1mgP64 national0.3%
- LithiumLi⁺0.02mgP12 national0.0%
- StrontiumSr²⁺0.04mgP13 national0.0%
- ManganeseMn²⁺0.03mgP19 national0.0%
- CopperCu²⁺—mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻686mgP83 national87%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻39.6mgP89 national10%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻7.2mgP9 national2%
- SulfateSO₄²⁻4.8mgP15 national0.8%
- Hydrogen phosphateHPO₄²⁻3.2mgP91 national0.5%
- FluorideF⁻0.50mgP30 national0.2%
- Hydrogen sulfidesulfur character — antibacterialHS⁻—mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃63.9mgP39 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.1mgP19 national
- ArsenicAs0.0010mgP6 national
- CadmiumCdNDmg
- ChromiumCrNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- 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.