曹Bicarbonate
A sodium-led bicarbonate spring — the classic jūsō-sen (soda-water) style, soft on the skin. At pH 8.5 it is alkaline, giving the slippery feel of Japan's beauty-water family. The source emerges as a cold-mineral spring at 21 °C and is heated for bathing.
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
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.
Cationsshare of charge (mval%)
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺626mgP79 national
- Potassiumminor; matters for drinking limitsK⁺11.2mgP47 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.5mgP10 national
- LithiumLi⁺1.8mgP90 national
- Magnesiummild; a laxative if you drink itMg²⁺0.80mgP24 national
- StrontiumSr²⁺0.80mgP76 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.20mgP39 national
- Manganesetrace; companion to iron springsMn²⁺NDmg
Anionsshare of charge (mval%)
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,541mgP94 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻90.3mgP38 national
- Fluoridetrace; drinking limits applyF⁻7.9mgP87 national
- HydroxideOH⁻3.6mgP97 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.70mgP18 national
- Bromidetrace, sea-originBr⁻0.30mgP36 national
- Iodideyellows in air; helps blood lipidsI⁻0.20mgP52 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻0.10mgP2 national
Non-dissociatedmeasured by mass
- Metaarsenious acidHAsO₂14.9mgP99 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂14.4mgP68 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃1.3mgP1 national
Dissolved gasesmeasured by mass
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂8.2mgP36 national
Measured at the source
Source temperature
21.0°C
Cold mineral
Tonicity
2.33g/kg
Hypotonic
Free CO₂
8.20mg/kg
Low
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.
- 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.