Naw, I wouldn't call them "bi-polar". My Green Ghost Ball Python-now THAT is bi-polar. You never know one day to next if he will be calm and allow handling or try to take your face off. Ditto for many of the Pituophis I've had, who'd be really sweet one moment and the next time you move they'd spazz out in that classic "hissy fit", and they remain like that, for their entire lives. With Water Snakes, IF they bite at all(and I've caught plenty that never attempted to bite, ever), it's pretty much a one-shot deal. They bite once or twice, and then figure out that it's a waste of time and effort and stop. They just don't try it again unless you cover yourself with fish oil. At the most, it's taken me 24 hours and just a few brief handling sessions to completely tame one to the point where it doesn't try to bite, musk or flee when I pick it up. I think with Water Snakes, if you grab them during capture, which most snake-catches tend to do, you're likely to be bitten, and honestly I can't blame the snake. Of course, the fact that they do tend to flee, FAST, at the slightest sign of danger means that often grabbing is the ONLY way to catch one before it vanishes into the water, but if you are able to lift up from underneath the snake without really grabbing it and just sorta let it "run" across your hands, you'll find that they are much, much less likely to even make that first defensive bite, and with gentle and persistent handling, in a few hours they will just give up on the whole defensive thing completely. I've reached into big boxes containing dozens of freshly wild-caught Water Snakes of various species that were being sold as feeder snakes at reptile shows, and picked out the ones I wanted(got most of my breeders that way) without getting a single bite. The most non-feed-response bites I've ever gotten from the same Water Snake was two. In contrast, a big male Corn I caught in the school building where I work a couple of years ago bit me no less than 18 times from the building to the parking lot where I had to go to get a snake bag out of my truck; my arms looked like I'd been in a fight with a bobcat by the time I got back in the building-scared my Principal half to death, lol! But, Corns are supposed to be the gentle snakes, while Water Snakes have the bad reputation for being "mean".Wow, I had no idea. All the experience with them that I have with them has been from wild specimens, which are far from tame.
That's really amazing that a snake can seem so vicious in the wild, and then, as oyu've pointed out, better than ball pythons in captivity. That's what I call one bipolar species.