A gentle simple thermal water: at 467 mg/kg of dissolved solids it is lightly mineralized and easy on the body, weakly alkaline and soft on the skin. Bicarbonate leads the anion side with chloride behind it, so the composition reads quiet rather than sharp. The one thing you notice is a faint sulfur note caught at the wellhead — the laboratory sample, tested 24 hours after collection, had gone completely odorless, so that trace of sulfur belongs to the water only while it is fresh from the source. The certificate defers indications and contraindications to a separate appendix that is not part of this document.
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⁺112mgP33 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺13.1mgP29 national12%
- Magnesiummild; a laxative if you drink itMg²⁺1.1mgP27 national2%
- Iron (II)Fe²⁺0.90mgP62 national0.5%
- PotassiumK⁺0.60mgP7 national0.3%
- StrontiumSr²⁺0.10mgP24 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻225mgP60 national59%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻53.2mgP27 national24%
- Fluoridetrace; drinking limits applyF⁻11.5mgP93 national10%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻16.4mgP29 national5%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻6.5mgP37 national2%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃21.8mgP6 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.1mgP36 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂40.3mgP64 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —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.