I cannot tell from this distance, but "water moccasins"/aka "cottonmouth" snakes are often confused with harmless water snakes, same thing where I live too.
I'd never kill either one, just relocate them.
http://ufwildlife.ifas.ufl.edu/water...mparison.shtml
https://www.youtube.com/watch?v=QuBlajsf714
https://www.youtube.com/watch?v=1oa6VziZH78
https://www.youtube.com/watch?v=_6Ao4lRlcuY