A gentle simple thermal spring in the hypotonic, neutral, high-temperature class, emerging at 73.1 °C — among Japan's hotter natural sources. Lightly mineralized and easy on the body, it is nonetheless rich in metasilicic acid, placing it in Japan's beauty-water family: the silica leaves a thin moisturizing film that makes skin feel smoother. The water is nearly colorless and clear, carrying a faint note of hydrogen sulfide and a whisper of metallic taste from its trace iron — real character for a spring classified as simple.
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⁺75.8mgP22 national57%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺19.0mgP37 national16%
- Potassiumminor; matters for drinking limitsK⁺36.9mgP80 national16%
- Magnesiummild; a laxative if you drink itMg²⁺4.1mgP44 national6%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺2.5mgP74 national2%
- LithiumLi⁺0.60mgP60 national2%
- AluminumAl³⁺0.20mgP64 national0.4%
- ManganeseMn²⁺0.60mgP68 national0.4%
- AmmoniumNH₄⁺0.30mgP39 national0.3%
- ZincZn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻192mgP63 national67%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻51.2mgP27 national24%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻25.6mgP16 national7%
- Fluoridetrace; drinking limits applyF⁻1.3mgP53 national1%
- BromideBr⁻0.30mgP37 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃75.3mgP45 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.9mgP28 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂33.4mgP62 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.90mgP74 national
- ArsenicAs0.01mgP24 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.