The private source at Ryoso Makibanoie is a simple thermal spring — weakly alkaline, hypotonic, and gentle on the skin. Dissolved solids come to just 718 mg/kg, so the water is light and unassertive: colorless and clear, almost tasteless, carrying only a very faint mineral note. What lifts it is silica — metasilicic acid at 215 mg/kg, generous enough to leave the thin moisturizing film that puts this water in Japan's beauty-water family.
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⁺108mgP30 national72%
- Magnesiummild; a laxative if you drink itMg²⁺8.2mgP58 national10%
- Potassiumminor; matters for drinking limitsK⁺24.6mgP69 national10%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺10.3mgP26 national8%
- LithiumLi⁺0.20mgP38 national0.5%
- ManganeseMn²⁺0.20mgP45 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻216mgP59 national51%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻81.2mgP35 national33%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻49.5mgP39 national15%
- Hydrogen phosphateHPO₄²⁻0.50mgP70 national0.1%
- FluorideF⁻0.20mgP16 national0.1%
- BromideBr⁻0.20mgP29 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃215mgP89 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.1mgP30 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂8.8mgP38 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.05mgP48 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.