A cold-mineral chloride spring (19.5 C at the wellhead, heated for bathing) led by sodium, calcium and magnesium. The 'iron-bearing' prefix on the certificate is earned — total iron 26 mg/kg, enough that the water emerges clear at the source and turns yellow-brown and slightly turbid by the time it reaches the lab. Neutral pH, moderately mineralized at 5.4 g/kg total solute, with a faint iron-rust note and a light salty-mineral taste on the lips.
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
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⁺941mgP85 national44%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺612mgP94 national33%
- Magnesiummild; a laxative if you drink itMg²⁺237mgP97 national21%
- FeTotalFe26.0mgP100 national1%
- ManganeseMn²⁺10.1mgP99 national0.4%
- PotassiumK⁺13.6mgP52 national0.4%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3,019mgP90 national93%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻314mgP67 national6%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻83.8mgP52 national2%
- BO2BO₂⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Fluoridetrace; drinking limits applyF⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- HSiO3HSiO₃⁻< —mg
- HydroxideOH⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃44.3mgP24 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.8mgP34 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂69.9mgP73 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.01mgP26 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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 (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Stress-related symptoms (sleep disorders and the like)
- Peripheral circulation disorders
- Cold sensitivity
- 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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.