A sodium-calcium chloride-sulfate spring with a sulfate sub-type adding quiet body. At pH 8.8 the water is alkaline, soft on the skin, and sits at the gentle end of Japan's 'beauty-water' tradition. Moderately mineralized at 5,640 mg/kg dissolved solids with notable metasilicic acid, it leaves a smooth feel after bathing.
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
Take care
- Active stage of any illness (especially with fever), active tuberculosis, advanced malignant tumor, severe anemia or other marked physical weakness, severe heart or lung disease causing shortness of breath on slight exertion, severe kidney disease with edema, gastrointestinal bleeding, visible bleeding, acute exacerbation of a chronic illness
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⁺1,269mgP89 national57%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺624mgP95 national
- Potassiumminor; matters for drinking limitsK⁺5.2mgP35 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻2,442mgP90 national78%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1,750mgP99 national26%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻517mgP77 national
- Fluoridetrace; drinking limits applyF⁻0.40mgP28 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃72.0mgP45 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂18.3mgP73 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
Measured at the source
On the certificate
- Chronic muscle or joint pain or stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like), muscle stiffness associated with motor paralysis, reduced gastrointestinal function (stomach heaviness and the like), mild hypertension, impaired glucose tolerance (diabetes), mild hypercholesterolemia, mild asthma or emphysema, hemorrhoid pain, autonomic nervous system instability, stress-related symptoms (sleep disorders and the like), convalescence, fatigue recovery, general health improvement
- Cuts, peripheral circulation disorders, cold sensitivity, depressed mood, dry skin
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.