A sodium-led bicarbonate spring — the classic 'jūsō-sen' style, soft on the skin in the Japanese 'beauty-water' family. Weakly alkaline, moderately mineralized at 2,400 mg/kg dissolved solids, and emerging hot at 53 °C from the source. A generous 85 mg/kg of metasilicic acid adds the silica-film feel that leaves skin noticeably smoother afterwards.
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
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）
- 活動性の結核、悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くようなより重い心臓又は肺の病気
- むくみのあるような腎臓の病気
- 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⁺571mgP78 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺31.1mgP46 national5%
- Magnesiummild; a laxative if you drink itMg²⁺16.8mgP69 national5%
- Potassiumminor; matters for drinking limitsK⁺29.4mgP74 national3%
- StrontiumSr²⁺1.4mgP82 national0.1%
- LithiumLi⁺0.10mgP29 national0.0%
- BariumBa²⁺0.10mgP53 national0.0%
- AluminumAl³⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,330mgP93 national75%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻200mgP65 national14%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻108mgP42 national10%
- FluorideF⁻0.70mgP40 national0.1%
- BromideBr⁻0.40mgP39 national0.0%
- BO2BO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- NitrateNO₃⁻0.0000mg0.0%
- HydroxideOH⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃85.4mgP48 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂30.3mgP79 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂199mgP89 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 筋肉若しくは関節の慢性的な痛み又はこわばり（関節リウマチ、変形性関節症、腰痛症、神経痛、五十肩、打撲、捻挫などの慢性期）
- 冷え性、末梢循環障害
- 胃腸機能の低下（胃がもたれる、腸にガスがたまるなど）
- 軽症高血圧、耐糖能異常（糖尿病）
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- 自律神経不安定症、ストレスによる諸症状（睡眠障害、うつ状態など）
- 病後回復期、疲労回復、健康増進
- きりきず、末梢循環障害、冷え性、皮膚乾燥症
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.