A sodium-led bicarbonate-chloride spring drawn at 58 °C — the bicarbonate side gives the classic 'jūsō-sen' soft, skin-smoothing feel while the chloride finish adds heat-retaining body. Weakly alkaline pH (7.9) puts it squarely in the Japanese 'beauty-water' family. The source is a blend of Totsukawa Onsen wells #2 and #7, shared across the Totsukawa hot-spring village including Hotel Subaru.
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
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
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
Gut & metabolic
Bicarbonate and sulfate waters, taken as a drink, neutralize stomach acid and help with constipation and gout.
stomach, gout (drinking)
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.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺440mgP73 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺17.4mgP36 national4%
- Potassiumminor; matters for drinking limitsK⁺22.2mgP66 national3%
- LithiumLi⁺1.3mgP85 national0.8%
- MagnesiumMg²⁺1.7mgP31 national0.7%
- AmmoniumNH₄⁺1.8mgP79 national0.5%
- Iron (II)Fe²⁺0.18mgP31 national0.0%
- BariumBa²⁺0.10mgP53 national0.0%
- ManganeseMn²⁺0.03mgP19 national0.0%
- AluminumAl³⁺0.01mgP19 national0.0%
- StrontiumSr²⁺NDmg
- ZincZn²⁺NDmg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻931mgP89 national64%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻293mgP63 national34%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻9.6mgP50 national1%
- Fluoridetrace; drinking limits applyF⁻4.6mgP77 national1%
- SulfateSO₄²⁻3.1mgP12 national0.3%
- Hydrogen phosphateHPO₄²⁻0.38mgP60 national0.1%
- Bromidetrace, sea-originBr⁻NDmg
- Hydrogen sulfidesulfur character — antibacterialHS⁻NDmg
- Iodideyellows in air; helps blood lipidsI⁻NDmg
- NitrateNO₃⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃23.0mgP8 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.5mgP23 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂26.0mgP56 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂SNDmg
- ArsenicAs0.0010mgP6 national
- CadmiumCdNDmg
- CopperCuNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
Measured at the source
On the certificate
- 胃十二指腸潰瘍
- 逆流性食道炎
- 高尿酸血症(痛風)
- 痙攣性胃炎
- 便秘
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.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Matsumoto S et al. Hot spring bathing and HbA1c in type 2 diabetes. J. JAPMC 73(3):163–170, 2010.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.