持世寺温泉 is a hot spring town in Yamaguchi, Japan. The water leaves the ground at 26.7–39.8°C, comfortably warm. It measures pH 8.1–8.9 — mildly alkaline, the slippery kind. Officially the water is classed as radioactive spring.
Radioactive spring
The water here
Radioactive spring 放射能泉
Contains trace radon that leaves the water quickly. Also called radium or radon springs.
The numbers
Water temperature
26.7–39.8°C
pH
8.1–8.9 (mildly alkaline)
Address in Japanese
山口県宇部市吉見持世寺 {{Location map many | Japan Yamaguchi Prefecture | relief = 1 | capt
Figures from the town's Japanese Wikipedia article.