A sodium-led chloride spring with sulfate adding quiet body and a bicarbonate softness layered in. Neutral in pH and moderately mineralized, it has a noticeable salt-driven warmth that lingers after the bath, the kind of heat-retaining chloride water that keeps you warm well after you step out. The source emerges hot at 59.7 °C in the Manganji district of Minamioguni.
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, nettō 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
- acute illness (especially with fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic diseases
- severe anemia
- other generally progressing illnesses
- pregnancy (especially early and late stages)
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⁺294mgP58 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺65.7mgP62 national
- Potassiumminor; matters for drinking limitsK⁺53.9mgP85 national
- Magnesiummild; a laxative if you drink itMg²⁺48.1mgP85 national
- Manganesetrace; companion to iron springsMn²⁺0.60mgP73 national
- LithiumLi⁺0.50mgP53 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.30mgP45 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻366mgP67 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻312mgP64 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻229mgP70 national
- Bromidetrace, sea-originBr⁻1.1mgP59 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.30mgP46 national
- Fluoridetrace; drinking limits applyF⁻0.20mgP19 national
Measured at the source
On the certificate
- chronic digestive disorders
- chronic skin diseases
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.