An alkaline simple thermal spring: hot at the wellhead (47 °C) yet only lightly mineralized at 791 mg/kg dissolved solids. At pH 9.0 it has the slippery, alkaline feel of Japan's beauty-water family, soft on the skin. Metasilicic acid is fairly generous at 111 mg/kg, leaving a thin silica film that smooths the skin. The water runs almost colorless and transparent, carrying a faint rotten-egg note of hydrogen sulfide.
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⁺196mgP51 national93%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺—mg5%
- Potassiumminor; matters for drinking limitsK⁺—mg2%
- Magnesiummild; a laxative if you drink itMg²⁺—mg1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻290mgP72 national65%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻148mgP51 national26%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻25.5mgP19 national8%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃112mgP59 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
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.