A calcium- and sodium-led sulfate spring. The wellhead is cold (14.7 °C, classified cold thermal spring) so the water is reheated before bathing. Alkaline at pH 9.06, it gives the slippery 'beauty-water' feel on the skin, and at 1,820 mg/kg of dissolved solids it has noticeable mineral body. Sensory reading at the wellhead is nearly colorless, nearly tasteless and nearly odorless.
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺321mgP89 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺233mgP56 national
- Potassiumminor; matters for drinking limitsK⁺1.9mgP22 national
- StrontiumSr²⁺1.7mgP84 national
- LithiumLi⁺0.19mgP32 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< 0.10mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1,180mgP97 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻40.5mgP25 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻21.0mgP69 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻15.5mgP10 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻1.3mgP73 national
- Fluoridetrace; drinking limits applyF⁻0.15mgP10 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃20.6mgP5 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂—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.
- 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.