This water rocket kit is part of the Learning in a Makerspace chapter of my new book "The Makerspace Workbench" from Maker Media! Simply 3D print the nozzle and cut out a set of fins to convert a soda bottle into a high-flying rocket.
Use 100% infill and keep the pressure low to prevent unintended explosion. For best results when launching, create a simple launcher that holds the NPT quick-release in place out of a piece of 3" PVC and an end cap. I would not recommend launching this with your hands. Be safe!