A weakly alkaline simple thermal spring with light overall mineralization (0.634 g/kg) but a respectable 60.9 mg/kg of metasilicic acid — enough to place it in the Japanese 'beauty-water' family with a subtly smoothing feel on the skin. On the anion side chloride and sulfate sit almost evenly matched, giving a sodium-led, clean-tasting profile rather than any one mineral character dominating.
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⁺153mgP40 national74%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺36.7mgP50 national20%
- Magnesiummild; a laxative if you drink itMg²⁺4.5mgP47 national4%
- Potassiumminor; matters for drinking limitsK⁺4.1mgP31 national1%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻164mgP52 national52%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻173mgP62 national40%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻30.7mgP19 national6%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻6.0mgP36 national2%
- Bromidetrace, sea-originBr⁻0.30mgP37 national
- Iodideyellows in air; helps blood lipidsI⁻0.10mgP35 national
- HydroxideOH⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃60.9mgP37 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.6mgP15 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂27.5mgP58 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.04mgP46 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.
- 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.