A sodium-led bicarbonate spring of the classic jūsō-sen style, emerging hot at 48 °C from a 160 m bore. Weakly alkaline at pH 8.3 with the soft, slippery touch that puts it firmly in Japan's beauty-water family. A generous 184 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards.
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⁺167mgP42 national64%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺35.4mgP49 national16%
- Magnesiummild; a laxative if you drink itMg²⁺21.4mgP71 national15%
- Potassiumminor; matters for drinking limitsK⁺15.7mgP54 national4%
- LithiumLi⁺1.1mgP76 national1%
- Iron (II)Fe²⁺0.40mgP48 national0.0%
- BariumBa²⁺0.20mgP74 national0.0%
- ManganeseMn²⁺0.20mgP45 national0.0%
- StrontiumSr²⁺0.20mgP44 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻532mgP77 national75%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻43.9mgP26 national11%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻51.3mgP39 national9%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻15.6mgP59 national5%
- FluorideF⁻0.10mgP9 national0.1%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃184mgP82 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.2mgP20 national
- Metaarsenious acidHAsO₂—mg
- LeadPb0.07mgP90 national
- CadmiumCd< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.