Besides all the myths, they eat rats,mice, small birds. Pretty much any warm blooded animal small enough.
What Do Water Moccasins Eat?
If you are not careful they try to eat you.
They are nasty creatures! They have been known to actually chase people, especially (lawn techs. In Florida).....and a lot of family pets go missing this way too! Small dogs, cats, rabbits, etc.
Some say that they eat people when my dad had a hotel he saw a man go near a nest and water splashed and no more