A sodium-calcium chloride-sulfate spring — salty and heat-retaining, with sulfate adding a quiet body underneath. It comes up at 65.3 °C, which puts it among Japan's hottest natural sources, and it is weakly alkaline and soft on the skin. A generous 197.6 mg/kg of metasilicic acid places it squarely in Japan's beauty-water family, leaving the kind of fine silica film that makes skin feel smoother. The water runs almost colorless and clear, with a slight saltiness and a faint sulfur note on the tongue; the certificate sampled it at the bath inlet rather than at the wellhead.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, netto 熱の湯).
cold sensitivity
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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⁺319mgP64 national73%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺80.8mgP66 national21%
- Potassiumminor; matters for drinking limitsK⁺33.3mgP77 national4%
- LithiumLi⁺0.90mgP72 national0.7%
- MagnesiumMg²⁺0.80mgP24 national0.4%
- StrontiumSr²⁺0.40mgP61 national0.1%
- ManganeseMn²⁺0.05mgP22 national0.0%
- AluminumAl³⁺0.02mgP22 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻462mgP74 national69%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻239mgP68 national26%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻51.0mgP29 national4%
- FluorideF⁻1.3mgP53 national0.4%
- BromideBr⁻2.1mgP72 national0.2%
- ThiosulfateS₂O₃²⁻0.40mgP61 national0.0%
- IodideI⁻0.60mgP73 national0.0%
- Hydrogen sulfideHS⁻0.05mgP20 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃198mgP85 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂66.9mgP93 national
- Metaarsenious acidHAsO₂1.6mgP92 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂5.3mgP29 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S—mg
- CadmiumCdNDmg
- ChromiumCrNDmg
- 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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.