A simple thermal spring rising from Nirayama Onsen Tochi Spring No. 3. At 29.2 °C it is a cold-mineral source, heated for bathing, and its weakly alkaline chemistry (pH 8.7) gives the soft, slippery feel of Japan's beauty-water family. Lightly mineralized and very gentle, it is the kind of low-temperature water suited to long, unhurried soaks — fitting for Hatake Onsen, a designated national health resort spring.
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.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺44.7mgP11 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺9.5mgP25 national
- Potassiumminor; matters for drinking limitsK⁺0.70mgP9 national
- Magnesiummild; a laxative if you drink itMg²⁺0.10mgP11 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.05mgP30 national
- CopperCu²⁺0.05mgP91 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.05mgP16 national
- Iron (III)Fe³⁺0.05mgP55 national
- Manganesetrace; companion to iron springsMn²⁺0.05mgP22 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻72.4mgP38 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻34.5mgP37 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻12.3mgP14 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻4.8mgP32 national
- HydroxideOH⁻0.09mgP39 national
- Bromidetrace, sea-originBr⁻0.05mgP7 national
- Iodideyellows in air; helps blood lipidsI⁻0.05mgP23 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃33.6mgP15 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.60mgP9 national
- Metaarsenious acidHAsO₂0.02mgP32 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.
- 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.