A sodium-led bicarbonate spring — the classic juso-sen style. Alkaline (pH 8.7), it gives the slippery, beauty-water feel on the skin and sits squarely in Japan's beauty-water family. At the wellhead the water is almost colorless and transparent, tasteless, with a faint hydrogen sulfide note.
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⁺273mgP60 national98%
- Potassiumminor; matters for drinking limitsK⁺5.5mgP36 national1%
- CalciumCa²⁺2.3mgP8 national0.9%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻608mgP81 national81%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻34.9mgP87 national9%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻39.2mgP24 national9%
- HydroxideOH⁻0.09mgP39 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂51.1mgP88 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.1mgP6 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.