勘七源泉Kanshichi Spring
A sodium-led bicarbonate spring — the classic jūsō-sen (soda-water) style, soft on the skin and squarely in the Japanese beauty-water family. A generous 207.5 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother. The well emerges at a scalding 94 °C, among Japan's hottest natural sources, yet reaches the bath undiluted at 100% source strength as free-flow with no recirculation.
Good for
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
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
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- active phase of illness (especially when feverish)
- active tuberculosis
- advanced malignant tumors or severe anemia and other cases of marked physical debilitation
- severe heart or lung disease causing breathlessness on slight exertion
- severe kidney disease with edema
- gastrointestinal bleeding
- when there is visible bleeding
- acute exacerbation of a chronic illness
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⁺204mgP51 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺8.1mgP23 national4%
- Potassiumminor; matters for drinking limitsK⁺13.6mgP52 national3%
- Magnesiummild; a laxative if you drink itMg²⁺4.3mgP45 national3%
- AmmoniumNH₄⁺4.7mgP91 national3%
- HydrogenH⁺0.20mgP59 national0.3%
- ManganeseMn²⁺0.20mgP45 national0.1%
- Iron (II)Fe²⁺0.10mgP30 national0.1%
- Iron (III)Fe³⁺0.20mgP66 national
- LithiumLi⁺0.20mgP40 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.10mgP54 national
- CopperCu²⁺0.10mgP96 national
- StrontiumSr²⁺0.10mgP26 national
- ZincZn²⁺0.10mgP72 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻505mgP76 national87%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻32.6mgP23 national10%
- Hydrogen phosphateHPO₄²⁻12.6mgP95 national3%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻4.9mgP15 national1%
- Iodideyellows in air; helps blood lipidsI⁻1.1mgP80 national
- BO2BO₂⁻0.10mgP38 national
- Bromidetrace, sea-originBr⁻0.10mgP15 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.10mgP11 national
- Fluoridetrace; drinking limits applyF⁻0.10mgP9 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.10mgP28 national
- HSiO3HSiO₃⁻0.10mgP43 national
- HydroxideOH⁻0.10mgP50 national
- SS²⁻0.10mgP95 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.10mgP45 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃208mgP87 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.2mgP25 national
- Metaarsenious acidHAsO₂0.10mgP56 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂110mgP81 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.10mgP61 national
Measured at the source
On the certificate
- chronic pain or stiffness of muscles or joints
- sensitivity to cold
- peripheral circulatory disorders
- reduced gastrointestinal function
- mild hypertension
- impaired glucose tolerance (diabetes)
- mild hypercholesterolemia
- mild asthma or emphysema
- hemorrhoid pain
- cuts
- peripheral circulatory disorders
- sensitivity to cold
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.