波佐見温泉・新源泉Hasami Onsen New Source
A sodium-led bicarbonate spring — the classic 'juso-sen' (soda-water) style. Weakly alkaline and soft on the skin, it sits in the Japanese beauty-water family. Moderately mineralized at 3.5 g/kg dissolved solids, the wellhead emerges at 37 °C — right at the threshold of a true hot spring, which makes for a comfortable long soak.
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
From a certificate analyzed in 2015.
- Active stage of any illness (especially with fever)
- Active tuberculosis, advanced malignant tumor, severe anemia or other marked physical weakness
- Advanced chronic illness, for example with shortness of breath on slight exertion
- Edema (from kidney disease, heart disease or other causes)
- Gastrointestinal bleeding, 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⁺879mgP84 national95%
- LithiumLi⁺0.70mgP63 national0.2%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺11.9mgP28 national
- Potassiumminor; matters for drinking limitsK⁺7.9mgP41 national
- Magnesiummild; a laxative if you drink itMg²⁺2.0mgP35 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻2,287mgP97 national85%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻231mgP59 national15%
- Fluoridetrace; drinking limits applyF⁻—mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂64.0mgP92 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃45.5mgP25 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂101mgP78 national
Measured at the source
On the certificate
From a certificate analyzed in 2015.
- Chronic muscle or joint pain or stiffness
- Muscle stiffness associated with motor paralysis
- Cold sensitivity
- Peripheral circulation disorders
- Reduced gastrointestinal function
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
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.