Municipal Kasugai Spring No. 1 is a gentle simple thermal spring, classified hypotonic and hot, whose wellhead pH of 9.7 marks it as strongly alkaline. The strong alkalinity gives a pronounced slippery feel on the skin, placing it squarely in Japan's beauty-water family. Sodium leads the modest mineralization alongside traces of chloride and sulfate; at the source the water carries a faint brownish-yellow tint and a metallic taste, emerging hot at 42.1 °C.
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
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⁺70.3mgP22 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺4.8mgP17 national7%
- PotassiumK⁺1.0mgP14 national0.9%
- AluminumAl³⁺0.10mgP54 national0.3%
- LithiumLi⁺0.10mgP29 national0.3%
- BariumBa²⁺0.0000mg0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- Iron (III)Fe³⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- MagnesiumMg²⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻54.2mgP28 national44%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻38.0mgP37 national23%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻22.5mgP71 national22%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻12.2mgP8 national6%
- BO2BO₂⁻3.6mgP79 national2%
- Fluoridetrace; drinking limits applyF⁻0.90mgP45 national1%
- HydroxideOH⁻0.80mgP84 national1%
- Hydrogen sulfideHS⁻0.30mgP47 national0.3%
- AsO2AsO₂⁻0.30mgP89 national0.0%
- BromideBr⁻0.10mgP15 national0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- HSO4HSO40.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- SS²⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃40.9mgP22 national
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.20mgP80 national
- 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.
- 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.