A simple thermal spring that reads strongly alkaline at the wellhead — pH 9.7 — while carrying only 165 mg/kg of dissolved solids, so the water is light on the body and the alkalinity does the work: it has the slippery, soap-like touch that places it squarely in Japan's beauty-water family. Colorless and transparent, it tastes faintly sweet straight from the source and carries a light sulfur note that the laboratory still recorded a full day after sampling. Fluoride, metasilicate and bicarbonate make up most of the small mineral load, giving a thin water more character than its totals suggest.
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⁺34.5mgP7 national88%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.4mgP12 national10%
- ZincZn²⁺0.40mgP91 national0.7%
- PotassiumK⁺0.30mgP3 national0.5%
- Iron (II)Fe²⁺0.20mgP38 national0.4%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻51.0mgP30 national34%
- Fluoridetrace; drinking limits applyF⁻10.9mgP92 national23%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻25.9mgP77 national18%
- HSiO3HSiO₃⁻27.2mgP70 national14%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻8.3mgP19 national7%
- Hydrogen sulfidesulfur character — antibacterialHS⁻1.3mgP71 national2%
- ChlorideCl⁻0.80mgP1 national0.9%
- Hydrogen phosphateHPO₄²⁻0.40mgP68 national0.3%
- ThiosulfateS₂O₃²⁻0.30mgP56 national0.2%
- NitrateNO₃⁻0.10mgP26 national0.1%
- AsO2AsO₂⁻0.08mgP73 national0.0%
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂35.2mgP62 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂SNDmg
- ArsenicAs0.06mgP54 national
- 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.