
Photo: Yanajin33 · CC BY-SA 3.0 · Wikimedia Commons
Kishū Kuroshio Onsen is a hot spring town in Wakayama, Japan. The water leaves the ground at 31.9°C, cool enough that the baths here are usually reheated. It measures pH 6.6 — close to neutral. Officially the water is classed as chloride spring.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Figures from the town's Japanese Wikipedia article.
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.