A sodium-calcium bicarbonate spring of the classic jūsō-sen style, soft on the skin. Neutral pH gives it a gentle feel, placing it squarely in Japan's beauty-water family. A generous 198 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⁺150mgP40 national53%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺53.4mgP59 national22%
- Magnesiummild; a laxative if you drink itMg²⁺29.6mgP76 national20%
- Potassiumminor; matters for drinking limitsK⁺18.3mgP60 national4%
- LithiumLi⁺1.3mgP84 national2%
- Iron (III)Fe³⁺0.70mgP83 national0.3%
- StrontiumSr²⁺0.30mgP52 national0.1%
- BariumBa²⁺0.20mgP71 national0.0%
- ManganeseMn²⁺0.10mgP36 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻549mgP79 national74%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻67.2mgP30 national16%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻60.9mgP46 national10%
- Hydrogen phosphateHPO₄²⁻0.40mgP68 national0.1%
- FluorideF⁻0.10mgP8 national0.0%
- BromideBr⁻0.10mgP14 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃198mgP85 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.9mgP35 national
- Metaarsenious acidHAsO₂0.20mgP68 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂90.3mgP77 national
- ArsenicAs0.12mgP67 national
- 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.