A gentle alkaline simple thermal spring blended from the Yumoto No. 58, 75 and 87 wells at Tonosawa. Its high pH gives the slippery feel of the Japanese beauty-water family, soft on the skin. Mineralization is light, but a respectable 69 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⁺89.0mgP26 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.02mgP22 national
- BariumBa²⁺< —mg
- CopperCu²⁺< —mg
- FeTotalFe< —mg
- LithiumLi⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- StrontiumSr²⁺< —mg
- ZincZn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻83.8mgP52 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻83.3mgP36 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻51.3mgP28 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻7.2mgP43 national
- NitrateNO₃⁻1.2mgP75 national
- Hydrogen phosphateHPO₄²⁻0.60mgP75 national
- Fluoridetrace; drinking limits applyF⁻0.19mgP10 national
- Bromidetrace, sea-originBr⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃69.0mgP43 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.6mgP34 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.10mgP12 national
- ArsenicAs0.15mgP71 national
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- various stress-related symptoms
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.