A sodium-calcium sulfate spring emerging hot at 45 °C. Moderately mineralized (2,217 mg/kg dissolved solids), it carries the quiet, settled body characteristic of sulfate waters.
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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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⁺337mgP65 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺292mgP88 national
- Potassiumminor; matters for drinking limitsK⁺15.5mgP54 national
- Magnesiummild; a laxative if you drink itMg²⁺7.0mgP57 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺5.1mgP80 national
- Manganesetrace; companion to iron springsMn²⁺0.30mgP53 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.10mgP54 national
- AmmoniumNH₄⁺0.10mgP24 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻853mgP94 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻361mgP69 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻208mgP55 national
- Fluoridetrace; drinking limits applyF⁻1.7mgP55 national
- Bromidetrace, sea-originBr⁻0.80mgP54 national
- Iodideyellows in air; helps blood lipidsI⁻0.50mgP69 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.10mgP11 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.10mgP28 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.10mgP45 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃64.5mgP40 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂10.6mgP58 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂59.7mgP72 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.30mgP69 national
Measured at the source
On the certificate
- Cold sensitivity
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.
- 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.