An alkaline simple thermal spring with very light mineralization (171 mg/kg of dissolved solids). At pH 9.3 the water sits firmly in Japan's beauty-water family, giving the characteristic slippery feel on the skin. The source emerges at 31.5 °C as a cold-mineral / low-temp spring, so the bath is reheated. Colorless, tasteless, and odorless — gentle and unobtrusive on the 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
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⁺43.5mgP11 national91%
- FeTotalFe< —mg
- Fluoridetrace; drinking limits applyF⁻11.2mgP93 national27%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻18.1mgP17 national23%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻30.5mgP18 national4%
- BO2BO₂⁻0.60mgP51 national0.5%
- HydroxideOH⁻0.60mgP78 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.7mgP8 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂< —mg
- 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
- 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.