湯Simple
An alkaline simple thermal spring at pH 9.25. Lightly mineralized at just 0.18 g/kg of dissolved solids, it is gentle on the body, yet the alkalinity gives the slippery, smooth feel of Japan's beauty-water family. Hypotonic and soft on the skin, it suits a long, unhurried soak.
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
On the certificate:recovery after illnessrecovery from fatiguepromotion of health
Take care
Contraindications
- acute illness (especially when accompanied by fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic diseases
- severe anemia
- other diseases generally in a progressing state
- 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.
Cationsshare of charge (mval%)
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺42.6mgP11 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.0mgP7 national
- Potassiumminor; matters for drinking limitsK⁺0.60mgP7 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.0000mg
Anionsshare of charge (mval%)
- Carbonatestrongly alkaline; slippery feelCO₃²⁻22.3mgP70 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻16.8mgP17 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻3.6mgP13 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻3.3mgP2 national
- HydroxideOH⁻1.6mgP92 national
- Fluoridetrace; drinking limits applyF⁻0.80mgP44 national
- BO2BO₂⁻0.50mgP50 national
Non-dissociatedmeasured by mass
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃42.8mgP24 national
Measured at the source
Source temperature
33.3°C
Warm
Tonicity
0.18g/kg
Hypotonic
On the certificate
- neuralgia
- muscle pain
- joint pain
- frozen shoulder
- motor paralysis
- stiffness of the joints
- bruising
- sprains
- chronic digestive disorders
- hemorrhoids
- sensitivity to cold
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.