A sodium-led bicarbonate spring, posted under its older classification name meaning "soda water containing common salt" — jūsō-sen in the traditional vocabulary. The bicarbonate gives the soft, smooth feel that places it in Japan's beauty-water family, while chloride, running to a little over 40 percent of the anion balance, adds a salty edge that helps warmth linger on the skin. Moderately mineralized rather than sharp, and the posted indications track the chemistry: chronic skin conditions, wounds and burns, alongside neuralgia and chronic rheumatoid arthritis.
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
- All acute illnesses, especially febrile conditions
- Progressive tuberculosis
- Malignant tumor
- Severe heart disease
- Bleeding disorders
- Severe anemia
- Other illnesses in an active or progressing stage
- Early and late pregnancy
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⁺—mg86%
- Potassiumminor; matters for drinking limitsK⁺39.1mgP80 national6%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺19.2mgP40 national6%
- Magnesiummild; a laxative if you drink itMg²⁺5.1mgP52 national3%
- AmmoniumNH₄⁺0.22mgP33 national0.1%
- Iron (II)Fe²⁺0.24mgP41 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻573mgP78 national56%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻252mgP61 national42%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻9.1mgP22 national1%
- CarbonateCO₃²⁻2.1mgP23 national0.4%
- HSiO3HSiO₃⁻2.2mgP47 national0.2%
- Hydrogen phosphateHPO₄²⁻0.59mgP70 national0.1%
- BO2BO₂⁻0.32mgP41 national0.0%
- H2PO4H₂PO₄⁻0.05mgP21 national0.0%
- HydroxideOH⁻0.01mgP25 national0.0%
On the certificate
- Hysteria and neurasthenia, especially in those prone to cranial congestion
- Wounds
- Burns
- Chronic skin conditions
- Chronic gynecological conditions (chronic cystitis, chronic adnexitis)
- Chronic rheumatoid arthritis
- Neuralgia
- Neuritis
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.