Although not the Northern Water Snake the closely related water snakes I’ve handled were significantly more defensively aggressive than what the video shows. As a rule most snakes have behavioral modes you can trigger to make even aggressive bitters appear tame, a lot like what you see in this video. But a lot of the water snakes I’ve handled wouldn’t shift into this behavioral mode when coaxed.
Here is an album where a copperhead came in the water just to check me out and then returned to the bank once it had investigated me. I didn’t get the pic on it’s closest approach to my leg because I didn’t want it to get the wrong idea, but they really aren’t interested in biting, just curious.
Here’s an album of an aggressive king snake, though it doesn’t appear aggressive in the photos, that I handled for a few minutes before releasing it.