A simple alkaline thermal spring rising in the hills of Ibigawa, Gifu Prefecture. The alkalinity gives it the slippery, soap-like feel that places it squarely in Japan's beauty-water family, and with dissolved solids of only about 0.36 g/kg the water is light and undemanding on the body. What lifts it above the ordinary simple spring is the sensory record on the certificate: colorless and clear to the eye, yet sulfurous on the tongue with a faint hydrogen sulfide note. A trace of sulfide ion sits behind that — barely enough to register on the analysis, but enough to give an otherwise unassuming water a whisper of sulfur character.
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⁺112mgP33 national94%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺5.5mgP18 national5%
- PotassiumK⁺0.70mgP9 national0.4%
- AmmoniumNH₄⁺0.20mgP29 national0.2%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- BariumBa²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- LithiumLi⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- StrontiumSr²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻108mgP56 national44%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻32.2mgP85 national21%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻29.7mgP20 national16%
- Fluoridetrace; drinking limits applyF⁻11.6mgP93 national12%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻18.0mgP12 national6%
- BO2BO₂⁻3.0mgP69 national1%
- Hydrogen sulfideHS⁻0.90mgP68 national0.6%
- AsO2AsO₂⁻< —mg
- Bromidetrace, sea-originBr⁻< —mg
- HSiO3HSiO₃⁻< —mg
- HSO4HSO4< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- HydroxideOH⁻< —mg
- SS²⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃42.7mgP23 national
- Metaarsenious acidHAsO₂< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.20mgP13 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —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.