A gentle simple thermal spring, piped in from System 2 of Beppu's municipal hot-spring supply on the Ishigaki line. It is mildly alkaline and soft on the skin, lightly mineralized and easy on the body — nothing sharp about it. What lifts it is silica: metasilicic acid at 179 mg/kg puts it squarely in Japan's beauty-water family, leaving the thin film that makes skin feel noticeably smoother afterwards. The sample was drawn from a catch basin inside the bathhouse rather than at the wellhead.
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⁺178mgP46 national82%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺12.5mgP29 national7%
- Potassiumminor; matters for drinking limitsK⁺20.0mgP62 national5%
- Magnesiummild; a laxative if you drink itMg²⁺4.6mgP49 national4%
- LithiumLi⁺1.7mgP89 national3%
- Iron (II)Fe²⁺0.10mgP30 national0.0%
- StrontiumSr²⁺0.10mgP26 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻183mgP52 national55%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻159mgP52 national28%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻73.3mgP49 national16%
- FluorideF⁻0.80mgP44 national0.4%
- NitrateNO₃⁻1.9mgP91 national0.3%
- BromideBr⁻0.50mgP47 national0.1%
- ThiosulfateS₂O₃²⁻0.10mgP45 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃179mgP79 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂7.9mgP49 national
- Metaarsenious acidHAsO₂0.20mgP70 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂6.6mgP33 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.13mgP69 national
- CadmiumCd< —mg
- 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.