A simple thermal spring in Misaka-cho, Fuefuki city. Strongly alkaline at pH 9.34 — slippery on the skin and sitting squarely in Japan's beauty-water family. Lightly mineralized (720 mg/kg dissolved solids), so the chemistry is gentle on the body; the wellhead runs hot at 51.8 °C and is pumped to surface.
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⁺189mgP48 national84%
- Potassiumminor; matters for drinking limitsK⁺0.50mgP5 national
- LithiumLi⁺0.10mgP29 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺—mg
- Magnesiummild; a laxative if you drink itMg²⁺—mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻16.4mgP10 national
- HSiO3HSiO₃⁻12.5mgP63 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻9.3mgP13 national
- Fluoridetrace; drinking limits applyF⁻2.1mgP59 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃47.3mgP26 national
- ArsenicAs0.27mgP86 national
- Radonfaint radon — studied for joint pain (hormesis)RnNDmg
- CadmiumCd< —mg
- CopperCu< —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.