Not a water moccasin. It's not just the shape of the head, a moccasin has a short stubby body compared to that snake.
Rat snakes will eat baby chicks as well as eggs. I leave them alone as long as they stay out of the eggs or baby chicks. If I can catch them I have permission to take them to a friend's place, she believes they will eat poisonous snakes and keep them away. Some snakes will, like a King snake, but I don't believe a rat snake will unless they are really small. Still, if I can catch them she gets them. I keep a pillow case, glove, and snake catching stick by the coop so I can be ready.
If I cannot catch them I will kill them if they are eating eggs or baby chicks in my brooder. But if they are not bothering my eggs or chicks I'm glad to have them around.