A blended chloride spring drawn from the Toyako Spa Cooperative's pooled wells — Toya nos. 5, 6, 9, 12 mixed with community wells 1 through 7 — and led by sodium and calcium. The pooled source runs hot at around 50 °C with a generous 1,400 L/min flow, and the 2,890 mg/kg of dissolved residue puts it firmly in the richly mineralized band that leaves a thin mineral film on the skin. A notably high 178 mg/kg of metasilicic acid layers a silica-softness on top of the usual heat-retaining grip of a chloride bath, so the warmth lingers well after you step out.
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
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
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
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⁺690mgP81 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺203mgP85 national
- Potassiumminor; matters for drinking limitsK⁺43.0mgP81 national
- Magnesiummild; a laxative if you drink itMg²⁺30.4mgP76 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,140mgP81 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻525mgP88 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻357mgP68 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃178mgP79 national
Measured at the source
On the certificate
- 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.
- 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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.