A bicarbonate spring led by sodium, with calcium and magnesium together carrying more than half of the cation load. It is neutral and hypotonic, colorless and clear at the spout, with a faint metallic tang on the tongue from the small amount of dissolved iron — and enough free carbon dioxide to sit just short of the carbonated-spring threshold. A generous 234 mg/kg of metasilicic acid places it squarely in Japan's beauty-water family, leaving the kind of silica film that makes skin feel smoother afterwards. The posted panel documents the water for cuts, burns and chronic skin conditions in the bath, and lists drinking uses for chronic digestive complaints, diabetes, gout and liver conditions.
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
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- Acute illness (especially with fever)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Any other illness in an actively progressing stage
- Pregnancy (especially the early and late stages)
- For the following conditions hot bathing (42 °C and above) is contraindicated as a rule: advanced arteriosclerosis, hypertension, heart disease
- Kidney disease
- Hypertension
- Any other condition involving edema
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⁺192mgP50 national37%
- Magnesiummild; a laxative if you drink itMg²⁺81.2mgP90 national30%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺120mgP78 national27%
- Potassiumminor; matters for drinking limitsK⁺40.1mgP81 national5%
- AmmoniumNH₄⁺2.1mgP82 national0.5%
- LithiumLi⁺0.70mgP63 national0.5%
- Iron (II)Fe²⁺2.5mgP76 national0.4%
- StrontiumSr²⁺0.50mgP68 national0.0%
- BariumBa²⁺0.10mgP50 national0.0%
- ManganeseMn²⁺0.10mgP36 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,050mgP92 national75%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻142mgP48 national17%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻79.4mgP52 national7%
- FluorideF⁻0.10mgP8 national0.0%
- BromideBr⁻0.30mgP37 national0.0%
- NitrateNO₃⁻0.20mgP42 national0.0%
- H2PO4H₂PO₄⁻0.10mgP32 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃234mgP92 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂24.0mgP77 national
- Metaarsenious acidHAsO₂0.20mgP68 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂836mgP98 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
- Cuts
- Burns
- Chronic skin conditions
- Chronic digestive disorders
- Diabetes
- Gout
- Liver disorders
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.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- 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.