A simple thermal spring — gentle in composition and easy on the body. It is mildly alkaline, so the water feels soft on the skin, and with only about 650 mg/kg of dissolved solids it stays light enough for a long, unhurried soak. Behind the plain classification the ion table leans sodium-calcium sulfate, though the concentrations remain modest: the posted analysis records the water as almost colorless and clear, tasteless and odorless.
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⁺142mgP39 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺56.5mgP60 national
- Magnesiummild; a laxative if you drink itMg²⁺3.4mgP41 national
- Potassiumminor; matters for drinking limitsK⁺0.70mgP9 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.10mgP29 national
- Manganesetrace; companion to iron springsMn²⁺0.10mgP37 national
- CopperCu²⁺0.0000mg
- Iron (III)Fe³⁺0.0000mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.0000mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻264mgP71 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻86.3mgP37 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻61.7mgP35 national
- Fluoridetrace; drinking limits applyF⁻4.6mgP76 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻3.8mgP28 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.20mgP36 national
- AsO2AsO₂⁻0.0000mg
- BO2BO₂⁻0.0000mg
- Bromidetrace, sea-originBr⁻0.0000mg
- HSO4HSO40.0000mg
- NitrateNO₃⁻0.0000mg
- HydroxideOH⁻0.0000mg
- SS²⁻0.0000mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃24.5mgP9 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.7mgP38 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.70mgP15 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CadmiumCd0.0000mg
- ChromiumCr0.0000mg
- Mercurytoxic trace — part of the drinking-safety checkHg0.0000mg
- LeadPb0.0000mg
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.