A sodium-calcium chloride spring — salty and heat-retaining as the chloride family always is, with a softer weakly alkaline finish that keeps the skin from feeling drawn. Moderately mineralized at 3,444 mg/kg dissolved solids, it carries enough body to leave warmth lingering well after the bath. Color, taste and odor are all neutral on the certificate, so the chemistry rather than the sensory profile is what shows up in the bath.
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, nettō 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
- 病気の活動期(特に熱のあるとき)
- Active tuberculosis
- 進行した悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少量の血液の混入も病状を悪化させるような疾患
- 急性腎不全
- 消化管出血
- 目に見える出血があるとき
- 慢性疾患の急性増悪期
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⁺782mgP80 national57%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺379mgP90 national32%
- Magnesiummild; a laxative if you drink itMg²⁺71.3mgP89 national10%
- PotassiumK⁺13.4mgP52 national0.6%
- StrontiumSr²⁺6.8mgP91 national0.3%
- AmmoniumNH₄⁺0.80mgP58 national0.1%
- BariumBa²⁺0.50mgP81 national0.0%
- AluminumAl³⁺0.10mgP57 national0.0%
- Iron (II)Fe²⁺0.10mgP31 national0.0%
- ManganeseMn²⁺0.10mgP39 national0.0%
- LithiumLi⁺0.10mgP27 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,900mgP84 national94%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻215mgP57 national6%
- SulfateSO₄²⁻11.1mgP25 national0.4%
- BromideBr⁻1.4mgP65 national0.0%
- FluorideF⁻0.20mgP19 national0.0%
- IodideI⁻0.60mgP73 national0.0%
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂60.0mgP91 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃35.0mgP18 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂36.7mgP65 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.10mgP56 national
- CopperCu0.0005mgP25 national
- ArsenicAs< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 筋肉若しくは関節の慢性的な痛み又はこわばり
- Muscle stiffness associated with motor paralysis
- Peripheral circulation disorders
- 胃腸機能の低下
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Peripheral circulation disorders
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.