An alkaline simple thermal spring with a wellhead pH of 8.6 — alkaline enough to give the slippery, soft-on-the-skin feel of Japan's beauty-water family. Lightly mineralized at 0.75 g/kg dissolved solids, it stays gentle on the body. A very faint note of hydrogen sulfide drifts up at the source.
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⁺210mgP55 national98%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.5mgP10 national1%
- PotassiumK⁺1.0mgP13 national0.3%
- LithiumLi⁺0.20mgP37 national0.3%
- Iron (II)Fe²⁺0.20mgP38 national0.1%
- AluminumAl³⁺0.10mgP55 national0.1%
- MagnesiumMg²⁺0.10mgP11 national0.1%
- BariumBa²⁺NDmg
- Iron (III)Fe³⁺NDmg
- Manganesetrace; companion to iron springsMn²⁺NDmg
- StrontiumSr²⁺NDmg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻360mgP69 national61%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻79.0mgP33 national23%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻45.0mgP39 national10%
- Fluoridetrace; drinking limits applyF⁻12.0mgP93 national7%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻12.0mgP53 national4%
- Bromidetrace, sea-originBr⁻0.20mgP28 national
- Iodideyellows in air; helps blood lipidsI⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃36.0mgP18 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂17.0mgP71 national
- Metaarsenious acidHAsO₂0.01mgP30 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂1.6mgP20 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.10mgP57 national
- ArsenicAs< —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.