At 9 weeks, your kitty is a little early for teething - but it could be. But they're also naturally bitey. And when kitty does begin to teethe, it'll just get worse. For our kitties, especially when they were teething, we used bendy straws, and I recommend them to everyone. Get bendy straws and litter your house with them.
As everyone has pointed out, do not "train" your kitty with any flicking, hitting, water or whatever. The minute kitty starts to bite, if kitty is in your lap, set him on the floor and give a short, sharp puff of air in the face and say NO sharply and sternly and walk away. This is the equivalent of a "hiss" from mom, and they learn quickly that this means "no" and what the word "no" means.
If you are playing with kitty and he starts biting, again, immediately stop, put the toy down, blow a short, sharp puff of air in the face and say "NO" sharply and sternly, and walk away. If there's a bendy straw within reach, pick it up and give it to kitty before you walk away.
The idea is both to communicate to kitty in a language he understands, teach him your language, and totally discourage unwanted behavior - yet give him something that can satisfy his need to bite.
Kitties are bitey by nature, but especially when they're teething. It is also the only way they have to tell you "no." If they don't want to be petted or touched anymore, they only way they can tell you is to give you a "bite." After the "puffing" method of training, our cats now put a paw on our hands instead of putting their mouths on our hands. And we understand they don't want to be petted anymore and we simply stop since they asked nicely.
The "air puff" method is a fabulous way of training kitty - to not bite, to not jump on the counters or where you don't want them, etc. Shelly still jumps on the counters - but he knows he's not supposed to, and the minute we walk into the kitchen and if he's up on one, he's out of the kitchen like a shot. He definitely learned what "no" means, he definitely understand it - and he's just like a 3 year old. He'll push the limits, and then tries not to get caught, lol!