Photo: BehBeh · CC BY-SA 3.0 · Wikimedia Commons
Yaita onsen is a hot spring town in Tochigi, Japan. The water leaves the ground at 76°C, hot. It measures pH 9 — strongly alkaline. Officially the water is classed as chloride spring, sulfate spring and iron spring.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Clear water with a faintly bitter taste. Known for holding heat.
Turns reddish brown as the iron meets air. The water is clear at the source.
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.