The Anasazi were making pots in the 1300's, but I suspect that a lot of their water carrying was done in gourds, and in baskets smeared with pitch. I believe they used the hot-rock method for a lot of their boiling. And I doubt that they ever set a clay pot on a fire to heat anything.

Bark containers can heat water as long as the flame doesn't touch the container ABOVE the water line. Below the water line the water itself, even if boiling, doesn't allow the container to get hot enough to burn. I would assume that this could hold true with gourds as well as birch bark.

I also suspect that the the Native Americans didn't do a great amount of boiling, and probably never boiled water just for drinking, since even the pioneers of the 1800s didn't realize that cholera & other diseases were usually passed around through contaminated water sources.

Sue