A sodium-led bicarbonate-chloride spring — the classic jūsō-sen (soda-water) style with a salty edge layered in from a chloride sub-type. Weakly alkaline and soft on the skin, it sits squarely in Japan's beauty-water family. It carries 141 mg/kg of metasilicic acid, leaving the kind of silica film that makes skin feel noticeably smoother. The wellhead runs at 88.3 °C — among Japan's hottest natural sources — and is cooled before bathing.
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⁺462mgP74 national94%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.8mgP19 national1%
- LithiumLi⁺1.3mgP85 national0.9%
- AmmoniumNH₄⁺1.2mgP68 national0.3%
- MagnesiumMg²⁺0.70mgP23 national0.3%
- StrontiumSr²⁺0.40mgP62 national0.1%
- AluminumAl³⁺0.0000mg0.0%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.0000mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.0000mg
- Manganesetrace; companion to iron springsMn²⁺0.0000mg
- ZincZn²⁺0.0000mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻955mgP90 national67%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻250mgP59 national30%
- Fluoridetrace; drinking limits applyF⁻9.0mgP89 national2%
- SulfateSO₄²⁻9.3mgP20 national0.8%
- ThiosulfateS₂O₃²⁻0.10mgP45 national0.0%
- AsO2AsO₂⁻0.0000mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.0000mg
- Hydrogen phosphateHPO₄²⁻0.0000mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.0000mg
- NitrateNO₃⁻0.0000mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃141mgP67 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂42.0mgP85 national
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂5.5mgP30 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.0060mgP17 national
- CadmiumCdNDmg
- ChromiumCrNDmg
- 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.
- 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.