An alkaline simple thermal spring at pH 8.5. Mineralization is light (263 mg/kg), yet the alkalinity places it in Japan's beauty-water family, giving a soft, slippery feel on the skin. The water is colorless and odorless, and at a source temperature of 28 °C it is classed as a cold thermal spring.
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⁺82.0mgP25 national95%
- Magnesiummild; a laxative if you drink itMg²⁺0.90mgP25 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺0.90mgP2 national1%
- PotassiumK⁺0.90mgP12 national0.5%
- LithiumLi⁺0.10mgP29 national0.3%
- StrontiumSr²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻113mgP45 national51%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻33.9mgP24 national26%
- Fluoridetrace; drinking limits applyF⁻14.0mgP96 national20%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻4.0mgP14 national2%
- Bromidetrace, sea-originBr⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂13.5mgP63 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃5.3mgP1 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S1.0mgP76 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- ArsenicAs0.0020mgP9 national
- Mercurytoxic trace — part of the drinking-safety checkHg0.0005mgP48 national
- CadmiumCd< —mg
- ChromiumCr< —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.