Collect the materials needed to build water rockets by using items that you have on hand or have students bring them from home. This project will require empty two-liter water bottles with their labels removed, card stock, a rubber stopper that fits into the neck of the bottle and a bicycle pump with a needle attachment.
The length of your rocket can vary based on how much power you would like it to have. The more space for air, the more distance you will have when you launch the rocket. Remove the top from one bottle and invert the bottle so that the bottom of the bottle becomes the top of the rocket. To add length, remove the tops and bottoms from additional bottles and tape them together with duct tape to make a long tube. Tape the top of one bottle to the bottom of the tube and insert a rubber stopper into it. Make a hole in the stopper just big enough to fit a bike pump needle into.
Give the project a more rocket-like appearance by making a nose cone and three fins out of card stock. These items will serve as decoration more than anything and they will not greatly impact the performance of the rocket.
To launch the rocket, you will need a stand to hold it that will give you enough distance between the bottom of the rocket and the ground to attach the nozzle of a bike pump. Cut a round hole in the top of a cardboard box large enough for the base of the rocket to fit through. Cut another hole into the side of the box and feed the pump tube through it.
Fill half of your rocket with water and insert the rubber stopper. Pull the pump nozzle through the hole in the box and insert the pump needle into the stopper. Set the rocket into place and stabilize the rocket by attaching a loose string around a wooden dowel or metal pole that is placed through the top of the box and into the ground. Move as far back as the pump tube will allow you to move and pump air into the rocket as fast as possible until it launches. Water rockets can be used over and over again unless they get torn or otherwise damaged. Be sure to launch your rocket in an area free of trees and buildings. Your rocket could launch as high as 600 feet into the air.