A sodium-led chloride spring. Wellhead pH is near neutral at 7.26 but the lab reading of 8.04 places it in the weakly alkaline class. The water is a clear dark-brown with a faint salty taste, moderately mineralized at about 8.4 g/kg dissolved solids. Hypotonic so the soak sits easy on the body, but it carries the heat-retaining, lightly mineral-coated finish characteristic of the old shokuen-sen (salt-spring) tradition.
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
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
Take care
- 病気の活動期(特に熱のあるもの)
- 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
- 少量の摂取でも発作を起こすような重い心臓又は肺の病気
- むくみのあるような重い腎臓の病気
- 消化管出血
- 目に見える出血があるとき
- 慢性の病気の急性増悪期
- 1日に80ml(よう化物イオンの含有量から算出される限界値)を超えて温泉を飲用する場合: 甲状腺機能亢進症
- 1日に430ml(ナトリウムイオンの含有量から算出される限界値)を超えて温泉を飲用する場合: 塩分制限の必要な病態(腎不全、心不全、肝硬変、虚血性心疾患、高血圧など)
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⁺2,743mgP93 national86%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺349mgP90 national12%
- Potassiumminor; matters for drinking limitsK⁺55.4mgP85 national1%
- MagnesiumMg²⁺7.9mgP58 national0.5%
- AluminumAl³⁺NDmg0.0%
- Iron (II)Fe²⁺NDmg0.0%
- ManganeseMn²⁺NDmg0.0%
- AmmoniumNH₄⁺1.4mgP72 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻4,288mgP92 national89%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻841mgP86 national10%
- Bromidetrace, sea-originBr⁻0.13mgP15 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻0.13mgP2 national
- Fluoridetrace; drinking limits applyF⁻0.01mgP2 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃19.4mgP5 national
- CopperCu0.06mgP96 national
- ArsenicAsNDmg
- CadmiumCdNDmg
- LeadPbNDmg
Measured at the source
On the certificate
- 筋肉痛、関節痛、五十肩、運動麻痺、関節のこわばり (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)
- Muscle stiffness associated with motor paralysis
- 胃腸機能の低下 (胃がもたれる、腸にガスがたまるなど)
- Mild hypertension
- 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、うつ状態、皮膚乾燥症
- 萎縮性胃炎、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.
- 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.