Japan officially classifies onsen water into 10 categories based on mineral content. Each offers unique therapeutic benefits.
Water Type Classifications
Chloride Springs
塩化物泉 (Enkabutsusen)
The most common type in Japan. Rich in sodium chloride with a warming effect that lasts long after bathing. Excellent for improving blood circulation and relieving muscle pain.
Simple Thermal Springs
単純温泉 (Tanjun Onsen)
Mild waters with low mineral content, making them gentle on the skin. Ideal for first-time onsen visitors and those with sensitive skin.
Sulfur Springs
硫黄泉 (Iousen)
Recognized by their distinctive smell. Known for treating skin conditions, improving metabolism, and antibacterial properties. Famous at Hakone and Kusatsu.
Bicarbonate Springs
炭酸水素塩泉 (Tansansuiso-ensen)
Known as "beauty water" for skin-smoothing effects. Helps remove dead skin cells and leaves skin feeling silky. Popular among women.
Sulfate Springs
硫酸塩泉 (Ryusan-ensen)
Excellent for treating high blood pressure and arteriosclerosis. Sometimes consumed for digestive health due to bitter taste.
Radioactive Springs
放射能泉 (Houshanousen)
Contains trace amounts of radon, believed to stimulate cellular activity. Safe levels, prized for treating rheumatism and gout.
Rare Water Types
Iron Springs (2.2%)
Rich in iron, often reddish-brown. Used for anemia treatment.
Carbon Dioxide (0.8%)
High CO2 creates bubbles on skin. Great for circulation.
Acidic Springs (0.8%)
Strong antibacterial properties. Kusatsu is famous for this type.
Aluminum Springs (0.1%)
Rarest type, found in volcanic regions.