Kyoekikai No. 4 Well comes out of the ground at 93.3 °C, among Japan's hottest natural sources, as a sodium-led chloride water with sulfate adding quiet body. It is almost colorless and clear, yet carries a faint hydrogen sulfide note at the spout and leaves a slight saltiness with a whisper of sulfur on the tongue. Weakly alkaline and generous with metasilicic acid at 232.7 mg/kg, it belongs to Japan's beauty-water family and leaves the kind of silica film that makes skin feel smoother afterwards. The posted composition panel lists it as documented for cuts, dry skin, poor peripheral circulation and cold sensitivity.
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
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
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Marked physical debilitation, such as advanced malignant tumor or severe anemia
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease with edema
- Gastrointestinal bleeding
- Any 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⁺404mgP72 national77%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺76.0mgP66 national17%
- Potassiumminor; matters for drinking limitsK⁺45.7mgP83 national5%
- LithiumLi⁺1.1mgP77 national0.7%
- MagnesiumMg²⁺0.30mgP16 national0.1%
- StrontiumSr²⁺0.30mgP52 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻566mgP77 national72%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻245mgP69 national23%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻41.0mgP26 national3%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻8.2mgP43 national1%
- FluorideF⁻1.8mgP57 national0.4%
- BromideBr⁻2.9mgP76 national0.2%
- ThiosulfateS₂O₃²⁻1.6mgP78 national0.1%
- IodideI⁻0.80mgP77 national0.0%
- Hydrogen sulfideHS⁻0.20mgP36 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃233mgP92 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂81.5mgP95 national
- Metaarsenious acidHAsO₂2.3mgP97 national
- CadmiumCdNDmg
- ChromiumCrNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
Measured at the source
On the certificate
- Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
- Reduced gastrointestinal function (heaviness, bloating)
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Stress-related symptoms (sleep disorders, depressed mood)
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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.