A blend of two wells in Katsuragi-no-sato, served as a sodium bicarbonate-chloride water with a salt-tinged finish from a chloride sub-type. Neutral pH and soft on the skin — the bicarbonate side does the smoothing work while chloride leaves a touch of mineral body. The wellhead runs cool at 28.4 °C, so the bath is reheated to 42 °C for soaking.
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
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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⁺2,018mgP91 national83%
- Magnesiummild; a laxative if you drink itMg²⁺103mgP92 national8%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺149mgP80 national7%
- Potassiumminor; matters for drinking limitsK⁺66.6mgP88 national2%
- AmmoniumNH₄⁺8.8mgP94 national0.5%
- AluminumAl³⁺0.10mgP54 national0.0%
- FeTotalFe0.07mgP33 national
- Manganesetrace; companion to iron springsMn²⁺0.07mgP24 national
- ZincZn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻3,836mgP99 national60%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,512mgP84 national40%
- CarbonateCO₃²⁻1.2mgP21 national0.0%
- NitrateNO₃⁻1.9mgP91 national0.0%
- SulfateSO₄²⁻1.2mgP8 national0.0%
- FluorideF⁻0.02mgP3 national0.0%
- IodideI⁻0.70mgP75 national0.0%
- Bromidetrace, sea-originBr⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂249mgP99 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃94.1mgP53 national
- Metaarsenious acidHAsO₂0.50mgP83 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂340mgP93 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.