A simple thermal spring blended from four wells in the Yamada district of Beppu, sampled from a relay tank rather than at the wellhead. Weakly alkaline and lightly mineralized at 890 mg/kg of dissolved solids, it is gentle on the body with very little chemical bite. At 70.7 °C the source ranks among Japan's hottest natural waters. What sets it apart is metasilicic acid at 156 mg/kg — enough to leave the thin silica film that places it squarely in Japan's beauty-water family, with noticeably smoother skin afterwards.
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⁺210mgP53 national81%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺18.0mgP37 national8%
- Potassiumminor; matters for drinking limitsK⁺22.0mgP66 national5%
- Magnesiummild; a laxative if you drink itMg²⁺5.3mgP51 national4%
- LithiumLi⁺1.4mgP86 national2%
- Iron (II)Fe²⁺0.10mgP30 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻270mgP60 national67%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻120mgP58 national22%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻73.0mgP36 national11%
- FluorideF⁻0.50mgP32 national0.3%
- BromideBr⁻1.2mgP63 national0.2%
- NitrateNO₃⁻0.70mgP67 national0.1%
- CarbonateCO₃²⁻0.20mgP12 national0.1%
- Hydrogen phosphateHPO₄²⁻0.10mgP34 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃156mgP70 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂11.0mgP58 national
- Metaarsenious acidHAsO₂0.30mgP76 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂3.2mgP24 national
- ArsenicAs0.15mgP71 national
- CopperCu0.01mgP76 national
- LeadPb0.01mgP46 national
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.