A textbook Hirugami-style alkaline simple thermal water, delivered as a blend of nine wells. Lightly mineralized (326 mg/kg dissolved solids) and gentle on the body, with the soft slippery feel that puts it in the Japanese 'beauty-water' family. The source emerges at a near-skin 36.3 °C, so it is reheated before bathing.
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⁺98.0mgP28 national96%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.4mgP13 national4%
- Aluminumshows up in acidic volcanic waterAl³⁺0.07mgP33 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.0050mgP11 national
- StrontiumSr²⁺0.0030mgP9 national
- BariumBa²⁺0.0010mgP27 national
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.0010mgP49 national
- LithiumLi⁺0.0010mgP11 national
- Magnesiummild; a laxative if you drink itMg²⁺0.0010mgP4 national
- Manganesetrace; companion to iron springsMn²⁺0.0010mgP14 national
- AmmoniumNH₄⁺0.0010mgP12 national
- ZincZn²⁺0.0010mgP33 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻45.0mgP90 national28%
- Fluoridetrace; drinking limits applyF⁻10.4mgP92 national10%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻19.5mgP12 national6%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1.4mgP9 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.0040mgP31 national
- Bromidetrace, sea-originBr⁻0.0010mgP6 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻0.0010mgP0 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.0010mgP19 national
- Iodideyellows in air; helps blood lipidsI⁻0.0010mgP22 national
- CadmiumCd< —mg
- ChromiumCr< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.