Carbon Dioxide Springs: "The Bubble Waters" — Indications & How to Bathe

Found near the Saga Yamato Interchange, "Yamato no Yu" stands as one of Kyushu's premier high-concentration carbonated springs. This source boasts an impressive 1600mg/kg of carbon dioxide gas, significantly surpassing the legal definition for a carbon dioxide spring of 1000mg/kg. Fresh, pump-lifted water is directly supplied, ensuring its purity. As you immerse yourself in the lukewarm bath, countless silver bubbles envelop your skin, their gentle effervescence stimulating circulation throughout your body. It's an ideal hot spring for those seeking deep relaxation and rejuvenation for both mind and body.

At the foot of Mt. Ontake, Yuya Onsen in Hida-Osaka is said to have served bathers for some three centuries, and locals still repeat the saying that carbonated spring water beats stomach medicine. Pumped from underground at around 12°C, the cold mineral water is rich in carbon dioxide and tastes like soda. Its iron content sends fine brown flakes drifting through the bath and gives the water a smooth, slightly slick feel. Carbon dioxide springs are rare in Japan, making this one a true local character.

Obuki is the roaring source at the heart of the steaming geothermal field of Tamagawa Onsen, on the southern slopes of Hachimantai. Its output from a single vent is often said to be the largest in Japan, and the fumarole field around it has long produced mineral deposits and the rare hokutolite stone. Every bath in the spa draws on this one source, served either straight or cut with fresh water. At pH 1.13 the water tingles sharply on the skin while warming the body to the core, and it has welcomed long-stay therapeutic bathers for generations, a spring for those who want to meet nature at full strength.

Nigoriyu bubbles up beside the Seri River in Nagayu Onsen, a village famed for carbonated springs, and was once known as the "high-temperature Ramune spring." Clear at the source, its iron content oxidizes into a tea-brown cloud in the bath, giving the spring its name. Around 40°C, the water lingers on the skin with fine bubbles and a silky, clinging feel, suiting bathers who want a long, gentle soak.

Said to date back to the Heian period and linked to the monk Gyoki, this sacred spring once welcomed pilgrims bound for Kumano. Its natural flow ceased for centuries until a 1965 boring struck water at 501 m, and today its calcium- and magnesium-rich water builds thick mineral crusts around every bath.

Kyowa Onsen opened in 1969 in Aibetsu, a town known for mushrooms. Its two sources, Chojuyu and Kyowayu, rise from the same spot and carry more than 1,800 mg/kg of free carbon dioxide, a rarity in Hokkaido. Because boiling would drive off the gas and alter the minerals, the inn pours the source straight from the tap into a small tub and adds hot water to reach bathing temperature, letting it flow without recirculation. The iron-tinged, yellowish water leaves fine bubbles on the skin for a smooth feel.

Obuki is the roaring source at the heart of the steaming geothermal field of Tamagawa Onsen, on the southern slopes of Hachimantai. Its output from a single vent is often said to be the largest in Japan, and the fumarole field around it has long produced mineral deposits and the rare hokutolite stone. Every bath in the spa draws on this one source, served either straight or cut with fresh water. At pH 1.13 the water tingles sharply on the skin while warming the body to the core, and it has welcomed long-stay therapeutic bathers for generations, a spring for those who want to meet nature at full strength.