re: Water moccasins are found mostly in the south. The northern terminus of their range is Dismal Swamp in southeastern Virginia
I grew up in the Shenandoah Valley of VA and we had a bunch of water moccasins**. They range a good bit north of SE Virginia. I hated the buggers. You always had to be on the lookout for 'em at my favorite swimming hole near Frank's Mill when I was but a tadpole.
** EDIT: I just read your post about banded water snakes. The snakes we had in the central Shenandoah Valley were dark (no discernable bands, IIRC) and their mouths were lightish (almost white) inside.