A sodium-led bicarbonate-chloride spring at 44.5 °C, weakly alkaline at pH 7.8 and soft on the skin. Moderately mineralized at 1,423 mg/kg total dissolved solids, the water carries a faint hydrogen sulfide note and a slightly acidic taste — a quiet, well-balanced bath rather than a chemistry showpiece.
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
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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⁺399mgP70 national95%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻219mgP57 national33%
- FluorideF⁻0.81mgP44 national0.6%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃36.3mgP18 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂61.5mgP73 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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.