A sodium-led chloride spring. Wellhead pH is near neutral at 7.26 but the lab reading of 8.04 places it in the weakly alkaline class. The water is a clear dark-brown with a faint salty taste, moderately mineralized at about 8.4 g/kg dissolved solids. Hypotonic so the soak sits easy on the body, but it carries the heat-retaining, lightly mineral-coated finish characteristic of the old shokuen-sen (salt-spring) tradition.
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 in which even a small intake can trigger an attack
- Severe kidney disease with edema
- Gastrointestinal bleeding
- Visible bleeding
- Acute exacerbation of a chronic illness
- Drinking more than 80 ml a day (the limit calculated from the iodide ion content): hyperthyroidism
- Drinking more than 430 ml a day (the limit calculated from the sodium ion content): conditions that require salt restriction (renal failure, heart failure, liver cirrhosis, ischemic heart disease, hypertension and the like)
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⁺2,743mgP94 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺349mgP91 national12%
- Potassiumminor; matters for drinking limitsK⁺55.4mgP86 national1%
- MagnesiumMg²⁺7.9mgP59 national0.5%
- AluminumAl³⁺NDmg0.0%
- Iron (II)Fe²⁺NDmg0.0%
- ManganeseMn²⁺NDmg0.0%
- AmmoniumNH₄⁺1.4mgP72 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻4,288mgP92 national89%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻841mgP87 national10%
- Bromidetrace, sea-originBr⁻0.13mgP14 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻0.13mgP2 national
- Fluoridetrace; drinking limits applyF⁻0.01mgP2 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃19.4mgP4 national
- CopperCu0.06mgP96 national
- ArsenicAsNDmg
- CadmiumCdNDmg
- LeadPbNDmg
Measured at the source
On the certificate
From a certificate analyzed in 2020.
- Muscle pain, joint pain, frozen shoulder, motor paralysis, joint stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like)
- Muscle stiffness associated with motor paralysis
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Autonomic nervous system instability, stress-related symptoms (sleep disorders, depressed mood)
- Convalescence, fatigue recovery, general health improvement
- Cuts, peripheral circulation disorders, cold sensitivity, depressed mood, dry skin
- Atrophic gastritis, constipation
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.