A sodium-led bicarbonate spring — the classic 'juso-sen' style, soft on the skin in the Japanese 'beauty-water' family. Weakly alkaline, moderately mineralized at 2,400 mg/kg dissolved solids, and emerging hot at 53 °C from the source. A generous 85 mg/kg of metasilicic acid adds the silica-film feel that leaves skin noticeably smoother afterwards.
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
From a certificate analyzed in 2021.
- Active stage of any illness (especially with fever)
- Active tuberculosis, malignant tumor, severe anemia or other marked physical weakness
- Severe heart or lung disease causing shortness of breath on slight exertion
- Kidney disease with edema
- Gastrointestinal bleeding, 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⁺571mgP79 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺31.1mgP46 national5%
- Magnesiummild; a laxative if you drink itMg²⁺16.8mgP69 national5%
- Potassiumminor; matters for drinking limitsK⁺29.4mgP74 national3%
- StrontiumSr²⁺1.4mgP83 national0.1%
- LithiumLi⁺0.10mgP27 national0.0%
- BariumBa²⁺0.10mgP49 national0.0%
- AluminumAl³⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,330mgP93 national75%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻200mgP65 national14%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻108mgP43 national10%
- FluorideF⁻0.70mgP38 national0.1%
- BromideBr⁻0.40mgP41 national0.0%
- BO2BO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- NitrateNO₃⁻0.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃85.4mgP48 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂30.3mgP79 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂199mgP88 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2021.
- Chronic muscle or joint pain or stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like)
- Cold sensitivity, peripheral circulation disorders
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension, impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Autonomic nervous system instability, stress-related symptoms (sleep disorders, depressed mood)
- Convalescence, fatigue recovery, general health improvement
- Cuts, peripheral circulation disorders, cold sensitivity, dry skin
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.