An alkaline simple thermal spring at around pH 9, classified as hypotonic and high-temperature. The water is almost colorless, transparent, tasteless and odorless, with the slippery feel of Japan's beauty-water family. A generous 76.8 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother, and the certificate lists general indications such as chronic skin conditions and recovery from fatigue.
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
Take care
- Acute phase of illness (especially when feverish)
- Active tuberculosis, advanced malignant tumors, or severe anemia and other serious diseases
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease accompanied by edema
- Gastrointestinal bleeding or visible bleeding
- Exacerbation phase of chronic disease
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⁺162mgP42 national88%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺17.6mgP37 national11%
- PotassiumK⁺2.2mgP23 national0.8%
- 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
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻193mgP65 national48%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻121mgP44 national41%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.0mgP63 national7%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻18.6mgP11 national4%
- HydroxideOH⁻0.20mgP66 national0.1%
- Hydrogen phosphateHPO₄²⁻0.10mgP34 national0.0%
- Bromidetrace, sea-originBr⁻0.09mgP9 national
- Iodideyellows in air; helps blood lipidsI⁻0.08mgP30 national
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃76.8mgP46 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.8mgP41 national
- Metaarsenious acidHAsO₂0.10mgP56 national
Measured at the source
On the certificate
- Chronic pain or stiffness of muscles or joints (chronic rheumatoid arthritis, osteoarthritis, low back pain, neuralgia, frozen shoulder, bruising, sprains in their chronic phase)
- Decreased gastrointestinal function (stomach heaviness, intestinal gas accumulation)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoidal pain
- Autonomic instability and stress-related symptoms (sleep disorders, depression, etc.)
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.