Hi, ex-cat breeder here. If your cat (kitten really) is lovely 90% of the time, then it's most likely play-fighting. It probably means he wasn't quite socialised enough at the pre-3 months stage, when all kittens are bitey-fighty and need to be taught by the breeder to not play this way with humans. It can be quite hard to alter some of these behaviours if that early window of opportunity is missed.
Of course, cats play-bite with their siblings all the time, so solution might be to get him a companion of a similar age?
If that's not possible, I would stop with the 'retaliation' water spray etc, because that could make it a much more threatening situation for him, which he'll respond to with aggression. Maybe just say 'no' angrily and distance yourself immediately?
We find largish stuffed toys useful for our current siamese kitten, similar age. We grab one and push it into her tummy when she gets a certain look in her eyes, and she kicks and bites the hell out of it. Access to outdoors is very useful too. Even a small run will do - just the sensations of sun, rain and wind make it interesting to them, and they will get to hunt and catch moths, spiders etc.
Also, if it's not actually getting worse, then maybe just give it a little more time? All cats calm down a lot after about 12 - 18 months especially when they are neutered.