A sodium-calcium sulfate spring of the settled, mineral-rich kind, classified hypotonic, alkaline, and high-temperature on the certificate. The alkaline pH gives the slippery, beauty-water feel that sits in the Japanese 'bihada-no-yu' family. Two wellheads run at 71.1 °C and 68.3 °C — among Japan's hottest natural sources — and a notable 62.9 mg/kg of metasilicic acid layers a thin silica film that leaves skin feeling smoother long after the bath.
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⁺471mgP75 national74%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺136mgP78 national25%
- Potassiumminor; matters for drinking limitsK⁺12.2mgP49 national1%
- Magnesiummild; a laxative if you drink itMg²⁺0.07mgP6 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.06mgP31 national
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1,111mgP97 national83%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻156mgP49 national16%
- BicarbonateHCO₃⁻6.8mgP4 national0.4%
- CarbonateCO₃²⁻2.4mgP26 national0.3%
- HydroxideOH⁻0.10mgP50 national0.0%
- Bromidetrace, sea-originBr⁻0.09mgP9 national
- Iodideyellows in air; helps blood lipidsI⁻0.07mgP27 national
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃62.9mgP38 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.1mgP52 national
- Metaarsenious acidHAsO₂0.50mgP83 national
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.
- 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.