A sodium-bicarbonate blended spring (a mix of the local 'tansan-sen' and 'kuroyu' sources). Weakly alkaline at pH 8.52 with a soft skin feel, in the juso-sen (soda-water) tradition. Hot at 61.7 °C at the wellhead, and still carrying 705.8 mg/kg of free CO₂ — the carbonated note the source name promises.
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
From a certificate analyzed in 2019.
- Active stage of any illness (especially with fever), active tuberculosis, advanced malignant tumor, or severe circulatory impairment from serious heart or lung disease, severe kidney disease with edema, gastrointestinal bleeding, visible bleeding, acute exacerbation of a chronic illness
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⁺194mgP51 national92%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻466mgP75 national80%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃233mgP92 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂706mgP98 national
Measured at the source
On the certificate
From a certificate analyzed in 2019.
- Cuts, peripheral circulation disorders, cold sensitivity, dry skin
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.