I have to say the stone pot is one of those things that peeves me just a bit. Seriously, lacking a pot to boil your water you don’t go and carve one from rocks, you throw some stones in your fire and, once they are hot enough, you dump them in the water. As long as you keep the rocks moving around, and don’t let them just sit at the bottom, the water even keeps the surface temp of the stones below ignition/melting point of most containers.
With a bit more skill you can even boil water in a brown paper lunch bag. The 249 degree difference between boiling point of water and the flash point of paper is more then enough to reach an equilibrium temp that keeps the out side of the bag dry, but unburned, while still allowing the water to reach boiling point.
At the very least you should be able to boil water in an empty tin can.
All of these are slower then a conventional pot. Perhaps a second clean water recipe could be used for such things, but with a much higher time cost?