A gentle simple thermal water, mildly alkaline and soft on the skin — squarely in the Japanese beauty-water family. It is colorless and clear with a faint hydrogen sulfide note and almost no taste. A generous 138 mg/kg of metasilicic acid leaves the kind of thin silica film that makes skin feel noticeably smoother. The source is exceptionally hot at 67.8 °C and is sampled from the storage tank inlet before reaching the bath.
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⁺190mgP45 national85%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺18.9mgP37 national10%
- Potassiumminor; matters for drinking limitsK⁺15.4mgP54 national4%
- LithiumLi⁺0.50mgP53 national0.7%
- StrontiumSr²⁺0.40mgP58 national0.1%
- AmmoniumNH₄⁺0.20mgP29 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻159mgP51 national26%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻57.4mgP44 national12%
- Fluoridetrace; drinking limits applyF⁻4.2mgP74 national2%
- ThiosulfateS₂O₃²⁻2.1mgP83 national0.4%
- Hydrogen sulfideHS⁻0.20mgP39 national0.4%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻10.2mgP49 national
- Bromidetrace, sea-originBr⁻0.60mgP48 national
- Iodideyellows in air; helps blood lipidsI⁻0.60mgP73 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻—mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃138mgP69 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.5mgP49 national
- Mercurytoxic trace — part of the drinking-safety checkHg0.02mgP97 national
- ArsenicAs< —mg
- CadmiumCd< —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.