A sodium bicarbonate spring — the classic juso-sen style, with sodium accounting for 98% of the cations. Alkaline at pH 8.5, it carries the slippery feel that places it squarely in Japan's beauty-water family. The certificate's sensory row records colorless, clear water with a faint hydrogen sulfide note and visible bubbling at the wellhead, over a moderate 1,362 mg/kg of dissolved solids.
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⁺367mgP68 national98%
- CalciumCa²⁺2.4mgP8 national0.7%
- MagnesiumMg²⁺0.90mgP25 national0.5%
- PotassiumK⁺2.7mgP25 national0.4%
- Iron (II)Fe²⁺0.20mgP38 national0.0%
- Aluminumshows up in acidic volcanic waterAl³⁺0.02mgP23 national
- Manganesetrace; companion to iron springsMn²⁺0.0030mgP14 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻860mgP88 national84%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻46.6mgP92 national9%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻22.1mgP17 national4%
- Fluoridetrace; drinking limits applyF⁻8.5mgP87 national3%
- Hydrogen sulfideHS⁻0.10mgP25 national0.0%
- SulfateSO₄²⁻0.10mgP2 national0.0%
- NitrateNO₃⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂28.0mgP79 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃23.4mgP8 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —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.