A sodium-led chloride-bicarbonate spring, neutral in pH and lightly turbid with a faint yellow-brown tint at the wellhead. The water carries a salty tang and a whiff of hydrogen sulfide, with bicarbonate softness layered into the chloride body. Moderately mineralized at 1,872 mg/kg, it lands in standard onsen-water territory rather than the extremes — a 34.8 °C source heated for bathing in central Kobe.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, netto 熱の湯).
cold sensitivity
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
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
From a certificate analyzed in 2020.
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Advanced malignant tumor, severe anemia or other marked physical weakness
- Severe heart or lung disease causing shortness of breath on slight exertion
- Kidney disease with 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⁺484mgP77 national82%
- Magnesiummild; a laxative if you drink itMg²⁺24.4mgP74 national8%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺34.2mgP48 national7%
- PotassiumK⁺12.9mgP50 national1.0%
- Iron (II)Fe²⁺0.90mgP62 national0.1%
- ManganeseMn²⁺0.50mgP66 national0.1%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- BariumBa²⁺< —mg
- LithiumLi⁺< —mg
- AmmoniumNH₄⁺< —mg
- StrontiumSr²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻446mgP74 national50%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻751mgP85 national49%
- Bromidetrace, sea-originBr⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Fluoridetrace; drinking limits applyF⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃70.1mgP44 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂17.1mgP71 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂75.7mgP75 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2020.
- Chronic muscle or joint pain or stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like)
- Muscle stiffness associated with motor paralysis
- Peripheral circulation disorders
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Stress-related symptoms (sleep disorders, depressed mood)
- Peripheral circulation disorders, cold sensitivity, depressed mood, dry skin (spring-type indications)
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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.