A bicarbonate spring carrying a balanced cation set of magnesium, sodium and calcium. Neutral pH and a moderately heavy 6,189 mg/kg of dissolved solids place it in the soft, skin-smoothing bicarbonate family that Japan calls the beauty-water tradition. The wellhead temperature of 30.9 °C makes it a cold-side spring that is reheated for bathing, and the water carries a faint metallic, slightly astringent edge on the tongue.
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.
- Magnesiummild; a laxative if you drink itMg²⁺347mgP98 national36%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺594mgP77 national33%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺455mgP91 national29%
- Potassiumminor; matters for drinking limitsK⁺36.9mgP79 national1%
- LithiumLi⁺4.4mgP95 national0.8%
- Iron (II)Fe²⁺7.2mgP86 national0.3%
- StrontiumSr²⁺7.1mgP92 national0.2%
- AmmoniumNH₄⁺1.9mgP78 national0.1%
- BariumBa²⁺0.40mgP79 national0.0%
- ManganeseMn²⁺0.30mgP58 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻4,561mgP100 national99%
- ChlorideCl⁻21.7mgP18 national0.8%
- SulfateSO₄²⁻0.50mgP5 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃141mgP68 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂11.9mgP58 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂921mgP98 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- 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.