A simple-type cold mineral spring that qualifies as an onsen on the strength of its metasilicic acid rather than any therapeutic anion. At pH 9.2 it is genuinely alkaline, giving the slippery, soft feel of Japan's beauty-water family. It carries 70.4 mg/kg of metasilicic acid, which leaves a thin silica film that makes skin feel smoother. Lightly mineralized and gentle on the body, and being a cold mineral source at 24.8 °C it is reheated for bathing.
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⁺27.6mgP6 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.1mgP12 national11%
- Potassiumminor; matters for drinking limitsK⁺1.4mgP17 national3%
- 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
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.3mgP65 national42%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻36.4mgP21 national41%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻6.2mgP17 national9%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3.6mgP5 national7%
- HydroxideOH⁻0.30mgP74 national1%
- Hydrogen phosphateHPO₄²⁻0.10mgP34 national0.0%
- BO2BO₂⁻< —mg
- Bromidetrace, sea-originBr⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃70.4mgP44 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.