Is there a way to judge with absolute certainty whether a rock will explode while boiling so long as it isn't next to a riverbed?

To me the biggest obstacle to living in the woods is hot water to shower and bathe, but if all you had to do was throw a few rocks into a small body of water this would heat up the water quickly and you'd have relatively easy access to hot water for stuff like this. The biggest thing is what are you going to make the tub out of because in the winter I don't think it's feasible to take showers unless you did next to a fire, I'm not sure. Also if you heat rocks and place them in a tub to bathe are they now no longer usable because they'd be full of water or would they still work again without exploding? http://ift.tt/2fMF6Rw