A sodium- and magnesium-led bicarbonate spring — soft, skin-smoothing water of the jūsō-sen (soda) style, sitting squarely in Japan's beauty-water family. Metasilicic acid is strikingly abundant at 270.7 mg/kg, leaving the thin silica film that makes skin feel noticeably smoother after the bath. The posted indications back up the skin story: cuts, burns and chronic skin conditions are listed alongside the usual recovery and circulation items. The poster also notes the source holds no drinking permit — this is bathing-only water.
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
- Acute illness (especially with fever)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Any other illness in an actively progressing stage
- 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⁺284mgP60 national64%
- Magnesiummild; a laxative if you drink itMg²⁺47.7mgP85 national20%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺43.7mgP55 national11%
- Potassiumminor; matters for drinking limitsK⁺21.1mgP65 national3%
- LithiumLi⁺1.4mgP86 national1%
- Iron (II)Fe²⁺0.70mgP58 national0.2%
- StrontiumSr²⁺0.30mgP55 national0.1%
- AmmoniumNH₄⁺0.10mgP24 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻959mgP90 national79%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻101mgP40 national14%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻64.7mgP45 national7%
- Hydrogen phosphateHPO₄²⁻0.40mgP69 national0.1%
- FluorideF⁻0.20mgP17 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃271mgP96 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂6.9mgP45 national
- Metaarsenious acidHAsO₂0.20mgP70 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂30.8mgP62 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
Measured at the source
On the certificate
- Neuralgia
- Muscle pain
- Joint pain
- Frozen shoulder
- Motor paralysis
- Joint stiffness
- Bruises
- Sprains
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
- Cuts
- Burns
- 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.
- 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.