A sodium-led bicarbonate spring — the classic jūsō-sen style — that also carries a weakly radioactive character. Weakly alkaline and soft on the skin, it sits in the Japanese beauty-water family. Dissolved solids of 1,940 mg/kg give it moderate, noticeable body. The bath is diluted to make up for limited source flow, reheated to a comfortable bathing temperature, and for hygiene it is served via recirculation and disinfected with silver ions and chlorine.
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⁺549mgP77 national98%
- CalciumCa²⁺2.8mgP11 national0.6%
- PotassiumK⁺5.0mgP34 national0.5%
- MagnesiumMg²⁺0.90mgP25 national0.3%
- Iron (II)Fe²⁺1.0mgP62 national0.2%
- LithiumLi⁺0.20mgP40 national0.1%
- StrontiumSr²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,133mgP92 national79%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻106mgP42 national13%
- Fluoridetrace; drinking limits applyF⁻25.0mgP99 national6%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.0mgP63 national3%
- SulfateSO₄²⁻3.8mgP13 national0.3%
- NitrateNO₃⁻0.10mgP25 national0.0%
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂67.6mgP93 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃29.0mgP12 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂7.3mgP34 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.