A simple thermal spring with one striking number behind it: metasilicic acid at 196 mg/kg. Dissolved solids are light at 0.93 g/kg, so the water itself is undemanding, and its mild alkalinity makes it soft on the skin — the silica is what places it in Japan's beauty-water family, leaving the kind of thin film that has skin feeling noticeably smoother afterwards. Sodium leads the cations and bicarbonate the anions, though both sit at modest concentrations. The sample was drawn from the site's storage tank rather than the wellhead.
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⁺126mgP35 national54%
- Magnesiummild; a laxative if you drink itMg²⁺25.8mgP74 national21%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺39.2mgP52 national19%
- Potassiumminor; matters for drinking limitsK⁺16.0mgP55 national4%
- LithiumLi⁺0.80mgP70 national1%
- ManganeseMn²⁺0.50mgP64 national0.2%
- Iron (II)Fe²⁺0.30mgP43 national0.1%
- BariumBa²⁺0.20mgP74 national0.0%
- StrontiumSr²⁺0.20mgP44 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻314mgP66 national49%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻141mgP46 national38%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻64.8mgP45 national13%
- Hydrogen phosphateHPO₄²⁻0.80mgP78 national0.2%
- BromideBr⁻0.40mgP39 national0.1%
- Fluoridetrace; drinking limits applyF⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃196mgP84 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.1mgP37 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂6.6mgP33 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.05mgP50 national
- 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.
- 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.