An alkaline simple thermal spring at the Chuo City Toyotomi Health & Welfare Center — gentle and soft on the skin. Alkaline (pH 8.4 at the wellhead, rising to 9.78 in the lab), it sits in the Japanese beauty-water family with a faintly slippery feel. The water is colorless, transparent, tasteless and odorless, with light hypotonic mineralization that goes easy on the body.
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⁺163mgP42 national65%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺74.9mgP65 national35%
- PotassiumK⁺0.70mgP9 national0.2%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻409mgP83 national79%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻38.6mgP25 national10%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.0mgP63 national6%
- HSiO3HSiO₃⁻32.6mgP71 national4%
- HydroxideOH⁻1.2mgP88 national0.7%
- BO2BO₂⁻2.4mgP71 national0.6%
- FluorideF⁻0.40mgP31 national0.2%
- Bromidetrace, sea-originBr⁻0.10mgP15 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —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.