A gentle simple thermal spring, weakly alkaline at pH 8.29 — soft on the skin, sitting in the Japanese beauty-water family thanks to its mild alkalinity. Lightly mineralized at 241 mg/kg of dissolved solids, it makes for an undemanding soak. The 29 °C source is a cold-mineral grade spring (under the 'low-temperature' class) reheated before bathing.
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
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⁺62.9mgP17 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.1mgP18 national8%
- MagnesiumMg²⁺0.30mgP16 national0.6%
- PotassiumK⁺0.50mgP5 national0.3%
- ZincZn²⁺0.02mgP47 national
- CopperCu²⁺0.0040mgP56 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- BariumBa²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- LithiumLi⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- AmmoniumNH₄⁺< —mg
- StrontiumSr²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻95.0mgP42 national50%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻24.0mgP17 national22%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.1mgP62 national19%
- Fluoridetrace; drinking limits applyF⁻3.3mgP67 national5%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻3.3mgP13 national2%
- Hydrogen phosphateHPO₄²⁻2.5mgP89 national1.0%
- BromideBr⁻0.50mgP48 national0.3%
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.80mgP65 national
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.4mgP7 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.2mgP20 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂3.7mgP25 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.02mgP36 national
- CadmiumCd< —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.
- 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.