A hot 53 °C blended source from Ito Onsen's Mizuochi cooperative, classified as a simple thermal spring with a total mineralization of 0.879 g/kg sitting just under the chloride-spring threshold. Sodium leads the cation profile while chloride and sulfate share the anion side almost evenly. Weakly alkaline at the wellhead (pH 8.4), it falls in the soft Japanese 'beauty-water' family — the water is nearly colorless and transparent, with no taste or odor, and a modest 57 mg/kg of metasilicic acid leaving skin smooth without the heaviness of a fully mineralized chloride bath.
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⁺201mgP51 national72%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺61.5mgP61 national25%
- Magnesiummild; a laxative if you drink itMg²⁺3.1mgP39 national2%
- PotassiumK⁺4.4mgP33 national0.9%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻381mgP80 national64%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻144mgP47 national33%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻22.7mgP14 national3%
- CarbonateCO₃²⁻2.4mgP26 national0.6%
- IodideI⁻0.20mgP52 national0.0%
- BromideBr⁻0.10mgP15 national0.0%
- HydroxideOH⁻0.04mgP35 national
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃57.3mgP34 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.6mgP16 national
- Metaarsenious acidHAsO₂0.10mgP41 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.