Definitely a non-venomous water snake. Banded water snakes often vary in pattern and coloration. I've caught hundreds of these and dozens of cottonmouths/water mocassins.
Take a look at the third photo down of a Florida banded water snake. Though this specimen's cross-bands are broken, they are very rectangular. You would never see rectangular or "uniform width" cross-bands on a cottonmouth. Yours just has unusually light "complete" cross-bands.
http://www.flmnh.ufl.edu/natsci/herpetology/fl-guide/Nerodiafpictiventris.htm
Okay, here are some pointers. The pupils appear round to me (water snake). Slit pupils "cat eyed pupils" would confirm a cottonmouth. This is not a golden rule for distinguishing venomous snakes from non-venomous snakes. But a definite determiner with water snakes and cottonmouths.
You can see the eyes from the top of the head (water snake). With cottonmouths this is impossible as they have "brows" extending over the eyes making it impossible them from above.
The photo of the snake in question shows the eyes protruding from angles at the sides of the head which would no doubt be visible if looking directly down at the head.
Perhaps the confusion lies in the "triangular" head. This is a typical "defensive" bluff with water snakes; head flattened out and rear jaw extended outward. Also, as oikos mentioned, the absence of pits. I don't see any either.
I do agree that if you can't 100% identify a snake, assume it is venomous. This is a golden rule and I mention this every time I give lectures on snakes. But you are asking for an I.D. This is no doubt a Florida water snake. I can differentiate them from cottonmouths at a glance. I certainly wouldn't say this if I wasn't 100% sure.