おかたの湯Okata-no-yu Hot Spring
A hot simple thermal spring (71.1 °C, neutral pH) — light in mineralization at 673 mg/kg dissolved solids, yet rich in metasilicic acid (195.7 mg/kg). Colorless and clear at the wellhead; by 24 hours after sampling the water has taken on a faint yellow-brown tint and a mild mineral note. The silica leaves the kind of thin film that makes skin feel noticeably smoother — the source sits squarely in the Japanese 'beauty-water' family.
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
- 病気の活動期(特に熱のあるとき)
- Active tuberculosis
- 進行性の悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くと息苦しくなるような重い心臓又は肺の病気
- 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⁺93.5mgP27 national66%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺30.8mgP46 national25%
- Potassiumminor; matters for drinking limitsK⁺9.9mgP45 national4%
- ManganeseMn²⁺0.20mgP45 national0.2%
- StrontiumSr²⁺0.20mgP44 national0.2%
- LithiumLi⁺0.01mgP11 national0.2%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺NDmg
- Magnesiummild; a laxative if you drink itMg²⁺NDmg
- AmmoniumNH₄⁺NDmg
- ZincZn²⁺NDmg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻270mgP62 national72%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻39.6mgP37 national13%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻28.9mgP22 national13%
- FluorideF⁻0.50mgP32 national0.5%
- ThiosulfateS₂O₃²⁻1.2mgP76 national0.3%
- Hydrogen sulfideHS⁻0.70mgP63 national0.2%
- BromideBr⁻0.10mgP15 national0.0%
- Iodideyellows in air; helps blood lipidsI⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃196mgP84 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.1mgP13 national
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
- Cold sensitivity
- Peripheral circulation disorders
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- 軽いコレステロール血症
- 軽いぜんそく又は肺気腫
- Hemorrhoid pain
- ストレスからくる諸症状(睡眠障害、うつ状態など)
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.