相玉地区4源泉・河内地区5源泉・蓮台寺地区2源泉・大沢地区2源泉・下田地区2源泉 計15源泉による混合泉Hamabe-no-Yu Blended Source (15 wells across Aitama, Kawachi, Rendaiji, Osawa and Shimoda)
A hot (53.3 °C) blended source pooling 15 wells from five Shimoda-area districts (Aitama, Kawachi, Rendaiji, Osawa and Shimoda), classified as a simple thermal spring with a quiet, well-balanced composition. The water is weakly alkaline (pH 8.1) and soft on the skin, sitting on the edge of Japan's beauty-water family. Lightly mineralized overall at 814 mg/kg, but a notable 346.5 mg/kg of sulfate — backed by 118.9 mg/kg of chloride — gives the bath more body than the simple-thermal label suggests.
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⁺146mgP39 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺89.6mgP68 national
- Potassiumminor; matters for drinking limitsK⁺9.3mgP44 national
- Magnesiummild; a laxative if you drink itMg²⁺1.4mgP29 national
- StrontiumSr²⁺0.40mgP62 national
- Manganesetrace; companion to iron springsMn²⁺0.10mgP36 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻347mgP78 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻119mgP44 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻25.7mgP15 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻1.2mgP21 national
- Fluoridetrace; drinking limits applyF⁻0.60mgP38 national
- Bromidetrace, sea-originBr⁻0.10mgP15 national
- HydroxideOH⁻0.02mgP28 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃69.3mgP43 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.50mgP8 national
- Metaarsenious acidHAsO₂0.01mgP33 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂4.4mgP29 national
- CadmiumCd< —mg
- 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.