Sodium-chloride-leaning blended source, but total dissolved solids sit at only 0.881 g/kg so the certificate classifies it as a simple thermal spring — hot category, 64.4 °C at the wellhead. Weakly alkaline (pH 7.7), gentle on the skin, with an unusually generous 116.9 mg/kg of metasilicic acid that leaves a thin silica film and makes the bath read like a textbook Japanese beauty-water source.
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⁺215mgP51 national79%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺37.9mgP50 national16%
- Potassiumminor; matters for drinking limitsK⁺18.6mgP60 national4%
- Magnesiummild; a laxative if you drink itMg²⁺2.0mgP37 national1%
- CopperCu²⁺0.05mgP91 national0.2%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻281mgP61 national67%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻133mgP59 national23%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻74.0mgP37 national10%
- Hydrogen phosphateHPO₄²⁻0.85mgP76 national0.2%
- Iodideyellows in air; helps blood lipidsI⁻0.07mgP28 national
- HydroxideOH⁻0.0090mgP26 national
- Bromidetrace, sea-originBr⁻NDmg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃117mgP62 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.1mgP12 national
- Metaarsenious acidHAsO₂0.03mgP35 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂8.8mgP35 national
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.