A sodium-calcium chloride spring with sulfate layered in for quiet body: salty, heat-retaining water at neutral pH and moderate mineralization (2,130 mg/kg). Metasilicic acid runs to 151.7 mg/kg, enough to leave the thin silica film that places this water in Japan's beauty-water family. The wellhead measures 74.6 °C, among Japan's hottest natural sources, and the certificate's appendix lists cuts, burns, chronic skin conditions, cold sensitivity and fatigue recovery among its documented bathing indications. Sekizenkan also keeps a drinking fountain fed by the same source, sampled and certified under its own analysis.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, netto 熱の湯).
cold sensitivity
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
Gut & metabolic
Bicarbonate and sulfate waters, taken as a drink, neutralize stomach acid and help with constipation and gout.
stomach, gout (drinking)
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- Acute illness (especially with fever)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Other illnesses in an actively progressing stage
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⁺474mgP76 national67%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺165mgP83 national27%
- Potassiumminor; matters for drinking limitsK⁺70.3mgP90 national6%
- MagnesiumMg²⁺1.6mgP30 national0.4%
- ManganeseMn²⁺0.70mgP72 national0.1%
- AluminumAl³⁺< —mg0.0%
- Iron (II)Fe²⁺< —mg0.0%
- AmmoniumNH₄⁺< —mg0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻754mgP79 national69%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻421mgP83 national28%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻41.2mgP25 national2%
- FluorideF⁻0.70mgP39 national0.1%
- CarbonateCO₃²⁻< —mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃152mgP69 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂54.4mgP90 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂18.7mgP50 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs1.5mgP97 national
- CopperCuNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
Measured at the source
On the certificate
- cold sensitivity
- chronic skin conditions
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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.
- Matsumoto S et al. Hot spring bathing and HbA1c in type 2 diabetes. J. JAPMC 73(3):163–170, 2010.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.