A simple thermal spring from Enzohara in Yamanashi City. At pH 9.5 it tips into the strongly alkaline range, giving the pronounced slippery feel that defines Japan's beauty-water family. Lightly mineralized at 158.6 mg/kg total dissolved solids, but a generous 51.3 mg/kg of metasilicic acid leaves a thin silica film that makes skin feel noticeably smoother afterwards.
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 feelCO₃²⁻26.5mgP81 national49%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻18.4mgP31 national21%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻12.3mgP13 national19%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻8.3mgP5 national8%
- Fluoridetrace; drinking limits applyF⁻0.40mgP28 national1%
- BO2BO₂⁻0.0000mg1%
- Hydrogen sulfideHS⁻0.0000mg0.6%
- NitrateNO₃⁻0.20mgP42 national0.2%
- BromideBr⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃51.3mgP29 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂26.0mgP55 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.01mgP29 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.