A sodium-led bicarbonate spring of the classic jūsō-sen style, with a chloride sub-type adding a salty edge. Weakly alkaline at pH 7.5 at the wellhead, it sits in Japan's beauty-water family, soft on the skin. The water emerges hot at 51.2 °C and carries 1,897 mg/kg of dissolved solids — moderately mineralised with the faint metallic-iron note and salty tang the certificate records at the source.
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⁺514mgP76 national93%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺11.9mgP28 national2%
- Magnesiummild; a laxative if you drink itMg²⁺4.3mgP45 national1%
- Potassiumminor; matters for drinking limitsK⁺12.7mgP49 national1%
- LithiumLi⁺1.5mgP88 national0.9%
- AmmoniumNH₄⁺2.7mgP85 national0.6%
- StrontiumSr²⁺1.1mgP79 national0.1%
- BariumBa²⁺0.40mgP81 national0.0%
- Iron (II)Fe²⁺0.20mgP39 national0.0%
- AluminumAl³⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,000mgP91 national67%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻286mgP62 national33%
- SulfateSO₄²⁻2.6mgP11 national0.2%
- FluorideF⁻0.30mgP24 national0.1%
- BromideBr⁻1.0mgP59 national0.0%
- AsO2AsO₂⁻0.0000mg0.0%
- BO2BO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- HSO4HSO40.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃45.0mgP25 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂11.7mgP60 national
- H2SO4FreeH2SO4Free0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂282mgP92 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CopperCu0.03mgP93 national
- ArsenicAs< —mg
- CadmiumCd< —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.