A sodium-led bicarbonate spring with a salty finish from a chloride sub-type — the classic jūsō-sen style softened by mild salinity. Weakly alkaline (pH 8.4) and gentle on the skin, it sits in Japan's beauty-water family. A cold-mineral source at 25.5 °C heated for bathing, with 1,342 mg/kg of dissolved solids giving the water moderate body.
Good for
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
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, nettō 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
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⁺402mgP70 national96%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺10.7mgP27 national3%
- MagnesiumMg²⁺1.8mgP33 national0.8%
- PotassiumK⁺2.2mgP23 national0.3%
- Iron (II)Fe²⁺0.40mgP48 national0.1%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻552mgP79 national49%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻302mgP64 national46%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻24.0mgP75 national4%
- SulfateSO₄²⁻7.4mgP18 national0.8%
- FluorideF⁻2.3mgP60 national0.6%
- Hydrogen sulfideHS⁻0.20mgP40 national0.0%
- Thiosulfateoxidized sulfurS₂O₃²⁻0.10mgP45 national
- BO2BO₂⁻< —mg
- HSiO3HSiO₃⁻< —mg
- HydroxideOH⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂19.4mgP74 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃17.7mgP4 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.
- 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.
- 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.