A sodium-magnesium-calcium bicarbonate spring, weakly alkaline and soft on the skin — the jūsō-sen (soda-water) style, which the certificate's older classification names an earth-alkali-bearing soda spring, and which sits squarely in Japan's beauty-water family. Metasilicic acid runs to a generous 222 mg/kg, leaving the kind of silica film that makes skin feel noticeably smoother afterwards. Mineralization is moderate at 1,022 mg/kg, with bicarbonate carrying nearly 80 percent of the anion balance. The sample was drawn not at a wellhead but from the storage tank that pools water from two well locations on the east and west sides of the same lot.
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
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⁺112mgP33 national47%
- Magnesiummild; a laxative if you drink itMg²⁺33.2mgP78 national26%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺48.0mgP57 national23%
- Potassiumminor; matters for drinking limitsK⁺13.0mgP50 national3%
- LithiumLi⁺0.70mgP64 national1.0%
- StrontiumSr²⁺0.30mgP55 national0.1%
- ManganeseMn²⁺0.20mgP45 national0.1%
- BariumBa²⁺0.10mgP53 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻503mgP76 national80%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻53.7mgP41 national11%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻34.0mgP24 national9%
- ThiosulfateS₂O₃²⁻0.20mgP55 national0.0%
- Fluoridetrace; drinking limits applyF⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃222mgP90 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.5mgP15 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂12.3mgP43 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.05mgP51 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.