A simple thermal spring drawn from Takaragawa's No. 3 well. Weakly alkaline and soft on the skin, lightly mineralized and gentle on the body. What lifts it above plain simple-thermal water is metasilicic acid — enough of it to leave the thin silica film that places this water in Japan's beauty-water family, with noticeably smoother skin afterwards. The site's pictorial map marks a statue of Yamato Takeru as the discoverer of Takaragawa Onsen.
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⁺135mgP37 national78%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺28.8mgP45 national19%
- Potassiumminor; matters for drinking limitsK⁺6.6mgP38 national2%
- MagnesiumMg²⁺0.21mgP15 national0.2%
- Iron (II)Fe²⁺0.25mgP39 national0.1%
- AluminumAl³⁺0.05mgP29 national0.1%
- ManganeseMn²⁺0.02mgP18 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻138mgP46 national50%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻130mgP59 national35%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻56.2mgP30 national12%
- Fluoridetrace; drinking limits applyF⁻4.1mgP72 national3%
- CarbonateCO₃²⁻0.30mgP14 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃87.5mgP50 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂15.1mgP68 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂2.2mgP22 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.37mgP90 national
- CopperCu0.0060mgP53 national
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
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.