They will eat anything from baby fish to full grown frogs.
Yes. All snakes are carnivores.
Mostly explained in the name, "Water" Snakes live in streams, etc.
yes.
Hawks and eagles have been commonly known and seen to eat water snakes, both poisonous and nonpoisonous. Wading birds eat water snakes if they see one in water. Crocodiles and alligators can eat water snakes of all sizes.
Yes alligators sometimes eat water snakes.
no, they only eat small animals. generally water snakes eat fish, but not trout
As far as Northern Water Snakes or Red-Bellied Snakes that live in the Northeastern US, smaller water snakes might be eaten by a raccoon, heron or hawk. There are other water snakes in other areas of the world, so this is a broad question.
no
Yes. Largemouth commonly eat small water snakes, and since smallies prey on basically the same food items, it is logical they will eat small snakes in the water.
fish and frogs
they will eat any small creatures. This includes fish, mice, frogs and water snakes.
Florida pine snakes eat mice and other things