A hot (49 °C) simple thermal spring drawn from a mixing tank that blends multiple wellheads on the property. Mineralization is light at 243 mg/kg dissolved solids, but the pH sits high at 9.1 — alkaline enough to give the slippery, soft-on-the-skin feel of the Japanese "beauty-water" family. The water is nearly colorless and clear, with no taste or odor, and is one of the rarer simple springs also approved for drinking.
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⁺58.9mgP17 national88%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.2mgP20 national11%
- Potassiumminor; matters for drinking limitsK⁺1.0mgP14 national1%
- Aluminumshows up in acidic volcanic waterAl³⁺0.06mgP31 national
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻48.2mgP39 national35%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻51.6mgP28 national29%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻24.3mgP19 national24%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻10.1mgP51 national12%
- HydroxideOH⁻0.20mgP66 national0.3%
- Fluoridetrace; drinking limits applyF⁻0.10mgP9 national
- Bromidetrace, sea-originBr⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃41.7mgP23 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.60mgP10 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —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.