A sodium-led alkaline simple thermal spring of light mineralization (0.214 g/kg total dissolved solids). pH measures 8.7 at the wellhead and 8.87 in the lab, putting it firmly in Japan's beauty-water family with a noticeably slippery feel on the skin. The source emerges at 29.8 degrees Celsius — a low-temperature spring that 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⁺25.2mgP5 national72%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.4mgP19 national21%
- Potassiumminor; matters for drinking limitsK⁺2.0mgP22 national3%
- Magnesiummild; a laxative if you drink itMg²⁺0.60mgP21 national3%
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻57.8mgP32 national61%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻7.2mgP43 national15%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻7.1mgP9 national13%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻7.6mgP18 national10%
- Bromidetrace, sea-originBr⁻0.20mgP29 national
- Hydrogen phosphateHPO₄²⁻0.10mgP33 national
- HydroxideOH⁻0.09mgP38 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃100mgP54 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.01mgP4 national
- Metaarsenious acidHAsO₂< —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.