有馬温泉 月光園 2号源泉Arima Onsen Gekkoen Spring No. 2
Gekkoen's house spring No. 2 in Arima. A sodium chloride water at roughly 6.5 g/kg total dissolved solids, moderately mineralized with a noticeable salty body and a thin mineral film on the skin after bathing. Weakly acidic at pH 6.4, with a tight, salt-tinged feel.
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
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
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺327mgP89 national18%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺1,788mgP90 national
- Potassiumminor; matters for drinking limitsK⁺84.1mgP90 national
- Magnesiummild; a laxative if you drink itMg²⁺18.1mgP69 national
- AmmoniumNH₄⁺1.3mgP70 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.10mgP30 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3,036mgP90 national84%
- Bromidetrace, sea-originBr⁻6.7mgP84 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃84.1mgP49 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂60.2mgP91 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂400mgP94 national
Measured at the source
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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.