i have always known you COULD boil water with hot rocks, but never done such a thing. there is some argument as to whether native americans actually ever made maple syrup this way. in theory, you can.
so anyway, boiling water with hot rocks from your fire is on the venture challenge this year. you KNEW that was going to figure in here somehow, right?
so anyway, i did this thing a number of times. the first time, my water ended up very, very dirty (but sanitary, because boiled) and everything would have needed to have decanted to be drinkable or usable for washing without a rinse in clean drinking water.
the second time i was more careful with where the rocks were placed in the fire, but fire is a messy business, and there's a lot of ash involved.
my rocks still came out varying degrees of dirty no matter where i placed them, although i figure with some clever wrapping in wide leaves or placement on some kind of shelf you might be able to get them to come out of the fire cleaner.
anyway, here's one of my trials. this isn't the best boil i got, but the best video.