A sodium-led bicarbonate spring of the classic jūsō-sen (soda-water) family. The source emerges cold at 14.7 °C, a cold-mineral spring heated for bathing. Weakly alkaline at pH 8.4 with the soft, slightly slippery feel that places it squarely in Japan's beauty-water tradition. Moderately mineralized at 3.49 g/kg total dissolved solids, the water carries a faint hydrogen-sulfide note and visible gas bubbles at the wellhead.
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⁺930mgP83 national98%
- CalciumCa²⁺8.0mgP23 national1.0%
- PotassiumK⁺11.9mgP48 national0.7%
- MagnesiumMg²⁺0.60mgP21 national0.1%
- Iron (III)Fe³⁺0.15mgP59 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.05mgP29 national
- Manganesetrace; companion to iron springsMn²⁺0.05mgP22 national
- CopperCu²⁺NDmg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻2,500mgP99 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1.2mgP1 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.50mgP16 national
- Bromidetrace, sea-originBr⁻0.25mgP30 national
- HydroxideOH⁻0.04mgP35 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.04mgP33 national
- Iodideyellows in air; helps blood lipidsI⁻0.04mgP23 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.7mgP8 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.22mgP6 national
- Metaarsenious acidHAsO₂NDmg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂8.0mgP35 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.20mgP68 national
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.