Anayu surfaces at a hot 60.4 °C as a simple thermal spring on the weakly acidic side (pH 3.22). Total dissolved solids are light at 568 mg/kg, but the water carries a generous 253 mg/kg of free CO2 and 157.7 mg/kg of metasilicic acid, giving the otherwise plain water a faint prickle and a touch of silica smoothness. A subtle hydrogen-sulfide note drifts off the surface as the bath stays warm well after exit.
Good for
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
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- 別表による
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⁺74.0mgP23 national57%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺14.8mgP32 national13%
- Aluminumshows up in acidic volcanic waterAl³⁺6.5mgP86 national13%
- Potassiumminor; matters for drinking limitsK⁺25.4mgP70 national12%
- Magnesiummild; a laxative if you drink itMg²⁺3.2mgP40 national5%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺3.0mgP76 national2%
- ManganeseMn²⁺0.60mgP68 national0.3%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻288mgP72 national78%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻58.1mgP30 national21%
- AsO2AsO₂⁻1.1mgP100 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃158mgP71 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂253mgP90 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S1.4mgP79 national
Measured at the source
On the certificate
- 別表による
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.
- 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.