A lightly mineralized simple thermal spring — 919.7 mg/kg of dissolved solids — pumped from a well in the Katayama district of Ikeda Town. At pH 8.8 the water is alkaline enough to feel soft and faintly slippery on the skin, which places it in Japan's beauty-water family. At the wellhead it runs colorless and clear, yet carries a very faint sulfur note and a metallic taste, so there is a little more character here than the clear water lets on.
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⁺258mgP59 national99%
- PotassiumK⁺2.9mgP26 national0.6%
- CalciumCa²⁺0.80mgP2 national0.3%
- FeTotalFe0.03mgP14 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.02mgP23 national
- Manganesetrace; companion to iron springsMn²⁺0.0030mgP14 national
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻581mgP80 national84%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻35.6mgP87 national11%
- Fluoridetrace; drinking limits applyF⁻7.2mgP84 national3%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻7.9mgP10 national2%
- NitrateNO₃⁻< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃21.8mgP6 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.7mgP27 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.