the water is minimal you put in the rocket. A gallon of wate ris about lbs and the amount in a rocket is no where near that, more like a few ounces (as the bottles they launch are usually about 20oz and we can essentially consider the plastic massless). Although they have a high velocity, the water weight is minimal so the momentum is relatively low. However, the momentum is not particularly relevant, more of the force that is required to launch the projectile (the grappling hook). I havent done the math but the force is fairly high in order to launch a object over 80 feet at a 70 degree (or greater angle). So you could probably calculate this all out and see, compared to a bottle rocket which is esentially massless once in flight, that the two forces are greatly different.
First of all, lads were only here for the craic! We have been through too much sh**e hawking over the past couple of thousand years to be goin all "rouge and sh**" and joining in fights we clearly don't want to be part of. It's like when a fisht fight breaks out in primary school between Vince and Iano Kelly. Most of us just watch, shout a bit and kick a bin to make noise or whatever, but we don't bother getting involved (well Vince is English so any sly opportunity for a shneaky kick to the shins and were all over it) we couldn't be a***d with the hole thing, we're simply too laid back.