A weakly alkaline simple thermal spring at a comfortable source temperature of 38.7 C. Total dissolved solids sit at a light 590 mg/kg, but metasilicic acid runs to 56 mg/kg, leaving the thin silica film that places this water squarely in Japan's beauty-water family. Radon at roughly 74 Bq/kg adds a quiet but real second dimension that the modest mineralization belies.
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⁺140mgP38 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺24.0mgP42 national
- Potassiumminor; matters for drinking limitsK⁺1.9mgP22 national
- Magnesiummild; a laxative if you drink itMg²⁺0.70mgP23 national
- StrontiumSr²⁺0.70mgP74 national
- LithiumLi⁺0.40mgP50 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.10mgP30 national
- Manganesetrace; companion to iron springsMn²⁺0.08mgP24 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻170mgP54 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻110mgP43 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻73.0mgP49 national
- Fluoridetrace; drinking limits applyF⁻1.9mgP57 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻1.4mgP22 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.40mgP62 national
- Bromidetrace, sea-originBr⁻0.30mgP36 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃56.0mgP34 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.8mgP41 national
- Metaarsenious acidHAsO₂0.10mgP56 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂2.2mgP22 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.08mgP61 national
- Radonfaint radon — studied for joint pain (hormesis)Rn—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.