A hot 58 °C simple thermal spring rising in the Kannawa quarter of Beppu. The pH sits at 7.6 at the wellhead and 6.6 in the lab — neutral overall, gentle on the skin. Total dissolved solids are a modest 830 mg/kg, but a generous 236 mg/kg of metasilicic acid leaves the kind of silky silica film that smooths the skin after a soak.
Good for
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
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.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺110mgP31 national52%
- Magnesiummild; a laxative if you drink itMg²⁺11.1mgP63 national12%
- Potassiumminor; matters for drinking limitsK⁺16.4mgP56 national5%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺47.8mgP57 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻278mgP63 national62%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻66.6mgP32 national24%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻53.5mgP41 national14%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃236mgP93 national
- Radonfaint radon — studied for joint pain (hormesis)Rn—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.
- 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.