He'll touch it, then if it doesn't burn his finger try to taste it. Anything he might notice? And yeah, he's using the bottle to get some volcano water in that case!

After that he'll still stick to the same path as detailed earlier, go to the spring to actually drink some water (keeping the volcano water in the bottle though!) then head toward the earlier spotted structure to the northeast. If he can't make it there before it gets dark, he'll be looking for a safe looking tree or hole between rocks to rest in and continue onward in the morning.