A hypertonic sodium chloride spring, salty with a distinct sweet note in the certificate's sensory test. Dissolved solids reach about 14.8 g/kg, so the water is richly mineralized and leaves a salt veil on the skin that keeps warmth in long after the bath. At the wellhead it emerges colorless and clear with visible gas evolution — free CO₂ measures 517.5 mg/kg — and the lab notes the water turns pale yellow and turbid within hours of sampling. The appended indications table documents it for cuts, peripheral circulation disorders, cold sensitivity, and dry skin.
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
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
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
From a certificate analyzed in 2023.
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Advanced malignant tumor or severe anemia with marked physical debilitation
- Severe heart or lung disease causing breathlessness 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⁺4,863mgP97 national88%
- Magnesiummild; a laxative if you drink itMg²⁺172mgP96 national6%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺266mgP88 national6%
- PotassiumK⁺64.5mgP88 national0.7%
- AmmoniumNH₄⁺4.2mgP90 national0.1%
- Iron (II)Fe²⁺4.4mgP82 national0.1%
- AluminumAl³⁺0.40mgP74 national0.0%
- ManganeseMn²⁺0.10mgP37 national0.0%
- ZincZn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻7,566mgP96 national89%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,654mgP95 national11%
- BromideBr⁻13.9mgP91 national0.1%
- SulfateSO₄²⁻1.3mgP8 national0.0%
- FluorideF⁻0.30mgP22 national0.0%
- IodideI⁻1.7mgP87 national0.0%
- CarbonateCO₃²⁻0.30mgP13 national0.0%
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂154mgP98 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃40.2mgP21 national
- Metaarsenious acidHAsO₂0.40mgP78 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂518mgP96 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2023.
- Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Stress-related symptoms (sleep disorders)
- Peripheral circulation disorders
- 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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.