A blended source drawing on the Nishizawa-no-Yu wells No. 1, 3 and 4. It carries no therapeutic spring-quality name: the posted analysis states the water qualifies as an onsen under Japan's Hot Spring Law purely because its metasilicic acid content clears the statutory limit at 66.1 mg/kg — the same silica that puts it in Japan's beauty-water family, leaving skin smooth rather than coated. Mineralization is light at roughly 0.24 g/kg and the pH sits at 6.0, so the water reads as mild and low-irritation. The source itself is a cold mineral spring at 15.5 °C, so it is reheated for bathing, held at temperature by recirculation and disinfected with a chlorine agent; no water is added except in emergencies.
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺32.2mgP46 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺8.8mgP2 national
- Magnesiummild; a laxative if you drink itMg²⁺4.5mgP46 national
- Potassiumminor; matters for drinking limitsK⁺1.4mgP16 national
- Manganesetrace; companion to iron springsMn²⁺0.08mgP25 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.03mgP14 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻85.6mgP40 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻38.3mgP36 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3.2mgP4 national
- Bromidetrace, sea-originBr⁻1.5mgP68 national
- Fluoridetrace; drinking limits applyF⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃66.1mgP41 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.40mgP7 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂132mgP83 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- LeadPb0.0020mgP23 national
- ArsenicAsNDmg
- CopperCuNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
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.