A gentle alkaline simple thermal spring. The high pH gives the slippery, soft-on-the-skin feel of Japan's beauty-water family, leaving skin smooth after a soak. It carries about 51 mg/kg of metasilicic acid, enough to leave a thin silica film that makes skin feel noticeably smoother. Lightly mineralized overall, it is an easy water for a long, unhurried bath.
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⁺33.6mgP7 national83%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.1mgP18 national14%
- Potassiumminor; matters for drinking limitsK⁺0.80mgP11 national1%
- Magnesiummild; a laxative if you drink itMg²⁺0.30mgP16 national1%
- AluminumAl³⁺0.0000mg0.0%
- BariumBa²⁺0.0000mg0.0%
- CopperCu²⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻26.5mgP80 national49%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻18.4mgP30 national21%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻12.3mgP15 national19%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻8.3mgP5 national8%
- BO2BO₂⁻1.0mgP60 national1%
- Fluoridetrace; drinking limits applyF⁻0.40mgP31 national1%
- Hydrogen sulfideHS⁻0.0000mg0.6%
- BromideBr⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- NitrateNO₃⁻0.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃51.3mgP30 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂26.0mgP56 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.01mgP28 national
- CadmiumCd< —mg
- ChromiumCr< —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.