A hot (57.2 °C) simple thermal spring — sodium and chloride dominate the ionic balance, but total dissolved solids (948.6 mg/kg) sit just below the 1,000 mg/kg threshold, so the certificate classifies it as simple thermal spring rather than a true chloride spring. Weakly alkaline at pH 7.9, soft on the skin, with a faint chloride character running underneath.
Good for
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
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⁺225mgP55 national68%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺87.5mgP68 national30%
- PotassiumK⁺4.2mgP32 national0.8%
- AmmoniumNH₄⁺0.30mgP40 national0.1%
- StrontiumSr²⁺0.60mgP72 national0.1%
- LithiumLi⁺0.40mgP50 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- BariumBa²⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻406mgP72 national78%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻136mgP60 national19%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻18.8mgP12 national2%
- FluorideF⁻1.1mgP49 national0.4%
- BromideBr⁻1.7mgP69 national0.1%
- IodideI⁻0.90mgP76 national0.1%
- CarbonateCO₃²⁻0.10mgP11 national0.0%
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃47.8mgP27 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂17.6mgP72 national
- Metaarsenious acidHAsO₂0.60mgP85 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.40mgP14 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.39mgP90 national
- CadmiumCdNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
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.
- 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.