River Birch = Water
Just an odd story. My mother has a couple of River Birches in her yard. I had to cut a few low hanging branches, no bigger in diameter than my thumb. They started dripping (which lasted for three or four days).
I got curious and put a coffee cup under one. It tasted like pure water and I'm guessing about as filtered as you can get, after going through the whole vascular system of a tree.
It struck me that it might be good in a survival situation. You'd be near water (hence the name) but I doubt water from the tree would have any parasites or amoebas.