The Karimizu Spring Geopark Nagasaki is officially classified as a Hot Spring because its temperature is above 24 degrees which is the cutoff point for whether a body of water is actually groundwater or not.
It's amazing to see nature at its best working efficiently and even more surprising that the water is cool to touch. At first, being that you are at a Hot Spring Resort and the spring water is bubbling at the surface, gives one the impression that the water is boiling at 100 degrees. However the shock of realizing that it is actually a reasonable temperature is gratifying. The spring water is actually safe to drink but trust me when I say it is not very pleasant. The carbonated water is clear but has a slight smell from the sulfide and thus is not really a delicious drink but by all means try for yourself, if you are game of course?
Check out the Karimizu Spring Geopark on a map: