湯Simple
An alkaline simple thermal spring at Ominesan Dorogawa. Lightly mineralized and gentle on the body, it is alkaline enough to give the slippery feel of Japan's beauty-water family, leaving skin smooth without any strong chemical edge.
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 fatiguehealth promotion
Take care
Contraindications
- acute illness (especially with fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic diseases
- severe anemia
- any other disease in an active progressive stage
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⁺15.0mgP3 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺4.0mgP15 national
- Magnesiummild; a laxative if you drink itMg²⁺0.54mgP20 national
- Potassiumminor; matters for drinking limitsK⁺0.42mgP4 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.13mgP54 national
- AmmoniumNH₄⁺0.10mgP24 national
- LithiumLi⁺0.05mgP17 national
- CopperCu²⁺0.01mgP71 national
Anionsshare of charge (mval%)
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻68.3mgP34 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻6.0mgP8 national
- Fluoridetrace; drinking limits applyF⁻0.94mgP46 national
Non-dissociatedmeasured by mass
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂27.1mgP78 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃26.4mgP9 national
Measured at the source
Source temperature
25.0°C
Low temp.
Tonicity
0.14g/kg
Hypotonic
On the certificate
- neuralgia
- muscle pain
- joint pain
- frozen shoulder
- motor paralysis
- stiffness of joints
- bruises
- 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.