A simple thermal spring distributed through Beppu City's municipal hot-spring supply network, arriving from a wellhead running at 68.5 °C — among Japan's hottest natural sources. It is neutral and only lightly mineralized (516 mg/kg dissolved solids), so the water itself is gentle on the body, though at the wellhead it carries a faint rotten-egg note of hydrogen sulfide. What lifts it above ordinary simple water is metasilicic acid at 124 mg/kg, enough to leave the thin silica film that places this spring in Japan's beauty-water family. Note that the sample for this certificate was taken at the bath 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⁺78.7mgP23 national62%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺20.7mgP39 national19%
- Magnesiummild; a laxative if you drink itMg²⁺10.1mgP62 national15%
- Potassiumminor; matters for drinking limitsK⁺8.4mgP42 national4%
- LithiumLi⁺0.30mgP41 national0.7%
- StrontiumSr²⁺0.20mgP42 national0.0%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻114mgP58 national42%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻60.3mgP29 national30%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻95.3mgP43 national28%
- ThiosulfateS₂O₃²⁻1.1mgP72 national0.3%
- FluorideF⁻0.40mgP28 national0.3%
- H2PO4H₂PO₄⁻0.30mgP73 national0.0%
- BromideBr⁻0.20mgP28 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃124mgP63 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.3mgP20 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂22.0mgP52 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.20mgP65 national
- ArsenicAs0.04mgP46 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.