A simple thermal spring blending two wells (Ami No. 221 and Yukawa No. 1), served at a community bathhouse in Yukawa, Ito City. Weakly alkaline at pH 8.4, it feels soft on the skin and sits in the Japanese beauty-water family. It carries 58.8 mg/kg of metasilicic acid, which leaves a thin silica film for noticeably smoother skin, and is classified as a hot spring at 42.3 °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⁺155mgP41 national82%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺74.2mgP65 national34%
- Magnesiummild; a laxative if you drink itMg²⁺3.8mgP43 national3%
- PotassiumK⁺3.7mgP30 national0.8%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻140mgP46 national35%
- CarbonateCO₃²⁻1.7mgP24 national0.5%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻384mgP70 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻314mgP75 national
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃58.8mgP35 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.0mgP30 national
- Metaarsenious acidHAsO₂0.09mgP41 national
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.