Water moccasins can become aggressive if they encounter a human that is trying to harm them or tries to mess with them or agitate them.
However water moccasins rarely do bite humans unless you get really close to them or they see you as a threat to them or there babies etc.
Water moccasins snakes will stand their ground and ward off a hum or other animal if you or the animal gets too close to the water moccasin.
They will protect themselves but as long as you leave the water moccasins alone and do not get to close the water moccasins will slither away from you or the animal without doing any harm.
I've been near water moccasin snakes and they've just went on their way and stayed away form me since I didn't touch them or try to get to close to them.