A sodium-led bicarbonate-chloride blend — the classic 'jūsō-sen' style softened by a chloride sub-type for a faintly salty edge. At the wellhead the water carries a yellow-brown tint with a hint of salt on the tongue and a faint H₂S note that fades within hours of sampling. Weakly alkaline and soft on the skin at 7.9 g/kg dissolved solids, it sits squarely in the Japanese 'beauty-water' family.
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⁺2,280mgP92 national99%
- PotassiumK⁺17.3mgP57 national0.4%
- MagnesiumMg²⁺3.4mgP40 national0.3%
- AmmoniumNH₄⁺2.9mgP86 national0.2%
- CalciumCa²⁺3.0mgP11 national0.1%
- AluminumAl³⁺1.2mgP78 national0.1%
- LithiumLi⁺1.0mgP74 national0.1%
- Iron (II)Fe²⁺3.2mgP77 national0.1%
- StrontiumSr²⁺0.70mgP74 national0.0%
- BariumBa²⁺0.10mgP53 national0.0%
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻4,104mgP100 national64%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,259mgP82 national34%
- Fluoridetrace; drinking limits applyF⁻22.2mgP98 national1%
- CarbonateCO₃²⁻19.6mgP67 national0.6%
- BromideBr⁻3.8mgP78 national0.1%
- SulfateSO₄²⁻1.1mgP8 national0.0%
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂117mgP96 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃30.5mgP13 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂11.6mgP42 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —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.