A gentle simple thermal spring rising in Ebino, neutral and hypotonic, with only about 376 mg/kg of dissolved solids — lightly mineralized and easy on the body. What lifts it above ordinary simple water is a generous 124 mg/kg of metasilicic acid, which leaves the kind of thin silica film that puts it in Japan's 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
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⁺60.7mgP17 national81%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.6mgP18 national9%
- Potassiumminor; matters for drinking limitsK⁺5.5mgP36 national4%
- Magnesiummild; a laxative if you drink itMg²⁺1.2mgP28 national3%
- AmmoniumNH₄⁺1.3mgP71 national2%
- LithiumLi⁺0.20mgP37 national0.9%
- Iron (II)Fe²⁺0.20mgP38 national0.3%
- Manganesetrace; companion to iron springsMn²⁺0.10mgP37 national
- BariumBa²⁺0.02mgP30 national
- StrontiumSr²⁺0.02mgP11 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.01mgP18 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻134mgP48 national70%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻35.1mgP37 national23%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻6.4mgP8 national6%
- FluorideF⁻0.30mgP22 national0.6%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃124mgP63 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.0mgP12 national
- Metaarsenious acidHAsO₂—mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂4.4mgP28 national
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.