A simple alkaline thermal spring whose water reaches pH 10.1 at the wellhead — strongly alkaline, with the slippery, soft feel of Japan's beauty-water family. Lightly mineralized at 248 mg/kg total dissolved solids, it is colorless and transparent, odorless, and carries only a very faint sweetness.
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⁺68.0mgP21 national97%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺1.2mgP4 national2%
- PotassiumK⁺0.90mgP12 national0.7%
- AluminumAl³⁺0.10mgP54 national0.3%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻71.3mgP96 national57%
- HSiO3HSiO₃⁻70.1mgP97 national22%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻19.1mgP12 national7%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻10.0mgP13 national7%
- Fluoridetrace; drinking limits applyF⁻4.2mgP72 national5%
- BO2BO₂⁻1.3mgP66 national0.7%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻0.20mgP3 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- HydroxideOH⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S1.3mgP79 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —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.