My vote is Diamondback Water Snake, and I've been a herpeto-phile since I was a little girl. Look at the photo bayouchica took, and then click on the small photo to the left of the title in the article webdawg linked. They look virtually identical, right down to the posture. The snake in question appears to be too long to bve a brown water snake, and the banding is definitely too distinct. The eyes being on top of the head, near the eye stripe, are some of the final keys that point to this almost certainly being a DWS.
While cottonmouths can have some pattern, it is not that distinct, either. Also, they have a shorter, wider body. Note that the cottnmouth has eyes on the sides of it's head (and of course, that distinctive "pit", although chica was not able to get a closeup of her snake's head. Please note that not all North American venomous snakes have a head wider than their body.
Lastly, it is definitely NOT a copperhead, but that photo of the copperhead is a BEAUTY!!!
Thanks for sharing, chica!