The water comes from the Tamagawa mineral spring, a wellhead in the Tamagawa district of Imabari, Ehime. At under 25 °C it is a cold-mineral source, so it is reheated for bathing. It is strongly alkaline and leaves the slippery, soft-skinned feel of Japan's beauty-water family, though the dissolved load is very light — the posted analysis records no spring-quality name at all (hypotonic, alkaline, cold mineral spring), meaning the water falls short of therapeutic-spring thresholds. The same posting states the baths are diluted with water, recirculated through a filtration unit, and disinfected with chlorine-based agents to meet Matsuyama City's public bath standards.
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
Take care
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Advanced malignant tumor, severe anemia, or other marked physical debilitation
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease with edema
- Gastrointestinal bleeding
- Any visible bleeding
- Acute exacerbation of a chronic illness
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⁺56.9mgP15 national97%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺1.0mgP2 national2%
- PotassiumK⁺0.20mgP1 national0.4%
- AluminumAl³⁺0.10mgP54 national0.4%
- LithiumLi⁺0.03mgP14 national
- BariumBa²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- AmmoniumNH₄⁺< —mg
- StrontiumSr²⁺< —mg
- ZincZn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻41.2mgP25 national25%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.8mgP68 national23%
- HSiO3HSiO₃⁻42.4mgP85 national20%
- Fluoridetrace; drinking limits applyF⁻9.0mgP90 national17%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻10.5mgP21 national8%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3.5mgP5 national4%
- HydroxideOH⁻1.0mgP86 national2%
- BO2BO₂⁻1.2mgP65 national1%
- Hydrogen sulfideHS⁻0.30mgP45 national0.4%
- Hydrogen phosphateHPO₄²⁻0.01mgP21 national
- Bromidetrace, sea-originBr⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
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.