Newtons 3rd law of motion: For every action, there is an equal and opposite reaction. How this applies to our bottle rockets that we constructed, is that when we release, the water and air pressure comes out of the bottom. That pushes against the ground, the equal and opposite reaction is the earth pushing back up. Whatever object has less mass moves. In this case, the rocket has less mass than what it is pushing against; the earth.
When we created our rockets, we had to keep all 3 laws of motion in mind for the best possible outcome. The 3rd law of motion is really crucial, without the reaction force of the earth pushing the water and air pressure upwards toward the sky, our action force would have no use. All forces come in pairs. For example, a person jumping into the air. The action force is their feet pushing on the ground, the reaction force is the ground pushing up on their feet. This allows the forces to correspond and allow the person to jump into the air. The same action-reaction forces is what allows our rocket to propel itself into the sky.
Knowing this information, you could alter the turnout of how your effective your rocket is by simply increasing or decreasing the amount of air pressure. The more air pressure that is compacted inside the bottle, the more force is exerted when the air and water push down on the ground. On the other hand, the less air pressure is built up, the less burst we will have because the reaction force will not be as great as it would if the action force was stronger.