An alkaline simple thermal spring (pH 9.2) emerging at 41.5 °C — a hot source by Japan's classification. Lightly mineralized at 670 mg/kg, it's gentle on the body, and the alkalinity gives it the slippery beauty-water feel typical of this style. The water is nearly colorless and clear at the wellhead, carrying a faint bitter taste and a slight rotten-egg note of H₂S — small carbonate and sulfide traces add quiet texture to an otherwise unobtrusive water.
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺90.9mgP70 national50%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺104mgP30 national49%
- PotassiumK⁺1.8mgP20 national0.6%
- StrontiumSr²⁺0.20mgP44 national0.1%
- MagnesiumMg²⁺0.04mgP5 national0.0%
- LithiumLi⁺0.03mgP14 national0.0%
- Aluminumshows up in acidic volcanic waterAl³⁺NDmg
- CopperCu²⁺NDmg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺NDmg
- Iron (III)Fe³⁺NDmg
- Manganesetrace; companion to iron springsMn²⁺NDmg
- AmmoniumNH₄⁺NDmg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻403mgP82 national93%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻7.8mgP44 national3%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻8.1mgP11 national3%
- BicarbonateHCO₃⁻4.9mgP3 national0.9%
- FluorideF⁻0.70mgP40 national0.4%
- Hydrogen sulfideHS⁻0.05mgP20 national0.2%
- Bromidetrace, sea-originBr⁻0.05mgP8 national
- BO2BO₂⁻NDmg
- Hydrogen phosphateHPO₄²⁻NDmg
- HSiO3HSiO₃⁻NDmg
- Iodideyellows in air; helps blood lipidsI⁻NDmg
- NitrateNO₃⁻NDmg
- HydroxideOH⁻NDmg
- Thiosulfateoxidized sulfurS₂O₃²⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃48.3mgP27 national
- Phosphoric acidH₃PO₄NDmg
- Metaarsenious acidHAsO₂NDmg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂NDmg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂NDmg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂SNDmg
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —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.