A simple alkaline thermal spring rising in the Tsurumi district of Beppu. Its mineral load is light, so the water reads gentle and low-irritation, with a soft, rounded feel rather than a heavy mineral bite. The alkalinity delivers the slippery touch that places this squarely in Japan's beauty-water family, and it is backed by an unusually generous 120.4 mg/kg of metasilicic acid, which leaves the kind of thin silica film that makes skin feel noticeably smoother afterwards. The wellhead itself ranks among Japan's hottest natural sources.
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⁺208mgP52 national91%
- Potassiumminor; matters for drinking limitsK⁺16.4mgP56 national4%
- LithiumLi⁺1.8mgP90 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.4mgP13 national2%
- MagnesiumMg²⁺0.40mgP18 national0.4%
- AmmoniumNH₄⁺0.30mgP40 national0.1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻173mgP62 national36%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻191mgP56 national32%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻53.4mgP92 national18%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻46.9mgP27 national13%
- FluorideF⁻1.1mgP49 national0.6%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃120mgP61 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.0mgP30 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.40mgP14 national
- ArsenicAs1.6mgP98 national
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.
- 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.