A gentle simple thermal spring, blended from the Kawaji No. 1 and No. 2 wells. It is weakly alkaline and only lightly mineralized — about 0.4 g/kg of dissolved solids — the kind of water that asks nothing of the bather. The certificate records it as almost colorless, clear, tasteless and odorless both at the source and again in the laboratory a day after sampling, so there is no smell or tang to work around during a long soak. Metasilicic acid at 49 mg/kg lends a touch of smoothness without tipping the water into the silica-rich bracket.
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⁺94.8mgP27 national81%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺16.5mgP34 national16%
- Potassiumminor; matters for drinking limitsK⁺3.8mgP30 national2%
- MagnesiumMg²⁺0.50mgP20 national0.8%
- StrontiumSr²⁺0.10mgP24 national0.0%
- BariumBa²⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻60.0mgP29 national35%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻74.1mgP48 national32%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻89.8mgP41 national30%
- Fluoridetrace; drinking limits applyF⁻2.9mgP66 national3%
- BromideBr⁻0.30mgP37 national0.0%
- AsO2AsO₂⁻0.0000mg0.0%
- BO2BO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- H2PO4H₂PO₄⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- HSO4HSO40.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃49.4mgP28 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂6.9mgP44 national
- Metaarsenious acidHAsO₂0.10mgP53 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂14.1mgP46 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CadmiumCd< —mg
- ChromiumCr< —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.