A gentle alkaline simple thermal spring (pH 8.9), drawn not from a single wellhead but from a tank that pools three Okudogo wells — No. 4-1, No. 9 and No. 13. Mineralization is light at 0.37 g/kg, so the water is easy on the body, yet the alkalinity gives the slippery feel of Japan's beauty-water family and 51.4 mg/kg of metasilicic acid leaves skin noticeably smoother. The posted panel lists the water for cold sensitivity and peripheral circulation disorders alongside the simple-spring indications of autonomic nervous system instability, insomnia and depressed mood. The bath itself is reheated, served via recirculation and disinfected with a chlorine-based agent, and the same panel notes that a herbal bath additive (yakusō-yu) is mixed in for its fragrance.
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
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
- Advanced malignant tumor, severe anemia, or other conditions of marked physical debility
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease accompanied by 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⁺112mgP32 national95%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.3mgP12 national3%
- LithiumLi⁺0.40mgP48 national1%
- PotassiumK⁺0.80mgP11 national0.4%
- AmmoniumNH₄⁺0.10mgP24 national0.2%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- BariumBa²⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- StrontiumSr²⁺< —mg
- ZincZn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻97.9mgP40 national55%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻59.3mgP33 national19%
- Fluoridetrace; drinking limits applyF⁻15.5mgP97 national16%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻15.3mgP27 national6%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻3.2mgP27 national2%
- ThiosulfateS₂O₃²⁻1.8mgP81 national0.6%
- HydroxideOH⁻0.10mgP49 national0.2%
- BromideBr⁻0.20mgP29 national0.0%
- Hydrogen phosphateHPO₄²⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃51.4mgP30 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂11.5mgP59 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.10mgP12 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
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)
- Muscle stiffness associated with motor paralysis
- Cold sensitivity
- Peripheral circulation disorders
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- 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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.