A sodium-led bicarbonate spring with a chloride sub-type adding a salty edge, emerging hot at 58 °C. At the wellhead the water carries a pale yellow-brown tint with a faint rotten-egg note and a salty tang on the lips. Weakly alkaline and soft on the skin, it sits in the Japanese "beauty-water" family, and a generous 171.6 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards.
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
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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⁺378mgP66 national79%
- Magnesiummild; a laxative if you drink itMg²⁺19.7mgP71 national8%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺31.4mgP49 national8%
- Potassiumminor; matters for drinking limitsK⁺33.6mgP76 national4%
- AmmoniumNH₄⁺2.5mgP82 national0.7%
- Iron (II)Fe²⁺1.2mgP67 national0.2%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.40mgP74 national
- StrontiumSr²⁺0.30mgP51 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.20mgP69 national
- BariumBa²⁺0.20mgP71 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻769mgP84 national62%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻274mgP62 national38%
- AsO2AsO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- HSO4HSO40.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- SulfateSO₄²⁻0.0000mg0.0%
- Bromidetrace, sea-originBr⁻0.80mgP55 national
- Hydrogen phosphateHPO₄²⁻0.60mgP75 national
- Fluoridetrace; drinking limits applyF⁻0.0000mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃172mgP79 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.6mgP24 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂60.5mgP73 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- 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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- 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.