A gentle simple thermal spring: neutral in pH and only lightly mineralized at 0.6 g/kg of dissolved solids, so it asks little of the body. What lifts it is silica — metasilicic acid at 182.7 mg/kg leaves the sort of thin film that puts this water squarely in Japan's beauty-water family. A faint sulfurous note comes off the surface, and the posted notice explains that the white flecks drifting in the tub are the spring's own minerals rather than impurities, with the bath refilled 365 days a year straight from the source. The panel lists the standard bathing indications, among them nerve, muscle and joint pain, cold sensitivity and fatigue recovery.
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⁺101mgP27 national76%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺18.1mgP37 national16%
- Potassiumminor; matters for drinking limitsK⁺15.7mgP54 national7%
- MagnesiumMg²⁺0.50mgP20 national0.7%
- ManganeseMn²⁺0.30mgP54 national0.2%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻103mgP41 national53%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻122mgP47 national37%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻18.0mgP31 national7%
- Fluoridetrace; drinking limits applyF⁻3.3mgP67 national3%
- Hydrogen sulfideHS⁻0.60mgP57 national0.4%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃183mgP82 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂7.0mgP45 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂29.0mgP58 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.80mgP73 national
Measured at the source
On the certificate
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
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.