A sodium-led bicarbonate spring with a chloride sub-type — the classic 'jūsō-sen' style softened by a salty edge. Weakly alkaline and gentle on the skin, it sits in the Japanese 'beauty-water' family. At the wellhead the water shows a yellow, faintly turbid cast with visible gas evolution, lifted as a 35 °C source by pump.
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⁺302mgP62 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺13.6mgP30 national5%
- Magnesiummild; a laxative if you drink itMg²⁺5.1mgP51 national3%
- PotassiumK⁺4.7mgP33 national0.8%
- Iron (II)Fe²⁺1.2mgP65 national0.3%
- AmmoniumNH₄⁺0.20mgP30 national0.1%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (III)Fe³⁺< —mg
- LithiumLi⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- StrontiumSr²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻538mgP78 national62%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻186mgP53 national37%
- CarbonateCO₃²⁻1.3mgP21 national0.3%
- BromideBr⁻0.30mgP36 national0.1%
- FluorideF⁻0.20mgP17 national0.1%
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃25.5mgP9 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂6.5mgP44 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂35.6mgP63 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.03mgP40 national
- 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.