A sodium chloride-bicarbonate spring — salty chloride water layered with a softer bicarbonate finish, classified under the old nomenclature as 'gan-jūsō-shokuen-sen' (salt water with sodium bicarbonate). The wellhead emerges at a cool 33.7 °C (a 'low-temp' classification requiring reheating for bathing), and the water is weakly alkaline and gentle on the skin. With 88.4 mg/kg of metasilicic acid it carries the silica-driven smoothness associated with Japan's 'beauty-water' family, and at 1,124 mg/kg of dissolved solids it offers moderate body without overwhelming mineralization — a balanced urban onsen.
Good for
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
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
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⁺315mgP63 national87%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺22.4mgP41 national7%
- Magnesiummild; a laxative if you drink itMg²⁺6.5mgP56 national3%
- Potassiumminor; matters for drinking limitsK⁺12.9mgP50 national2%
- AluminumAl³⁺0.40mgP74 national0.3%
- AmmoniumNH₄⁺0.40mgP43 national0.1%
- BariumBa²⁺0.20mgP74 national0.0%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- LithiumLi⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻361mgP69 national67%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻7.5mgP18 national1%
- BromideBr⁻0.70mgP51 national0.1%
- IodideI⁻0.20mgP52 national0.0%
- Hydrogen phosphateHPO₄²⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃88.4mgP50 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.40mgP8 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂12.0mgP43 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —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.