A sharp, prickly acidic spring (pH 2.5 at the source) that is also markedly iron-rich, oxidizing reddish-brown on contact with air. At the wellhead the water carries a red tint with a strong metallic iron note in taste and smell. With total iron around 30 mg/kg it bites a little on the skin, and as a cold-mineral source below 25 °C it is reheated for bathing.
Good for
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
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.
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺3.2mgP75 national37%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺36.9mgP50 national21%
- Aluminumshows up in acidic volcanic waterAl³⁺14.3mgP91 national18%
- Iron (III)Fe³⁺22.5mgP99 national14%
- Magnesiummild; a laxative if you drink itMg²⁺4.2mgP44 national4%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺7.9mgP85 national3%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺2.3mgP0 national1%
- ZincZn²⁺0.0000mg0.4%
- ManganeseMn²⁺0.50mgP64 national0.2%
- PotassiumK⁺0.50mgP5 national0.1%
- LithiumLi⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- StrontiumSr²⁺0.10mgP26 national
- BariumBa²⁺0.0000mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻343mgP77 national95%
- HSO4HSO436.5mgP61 national5%
- FluorideF⁻0.40mgP31 national0.3%
- H2PO4H₂PO₄⁻0.40mgP83 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃29.1mgP12 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.20mgP6 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂52.0mgP70 national
- CopperCu0.12mgP100 national
- ArsenicAs0.06mgP53 national
- LeadPb0.01mgP46 national
- CadmiumCd< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.
- 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.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official