Every technical challenge, when satisfied, requires that it be superceded by yet another of greater magnitude. When you have mastered the use of single-stage water rockets, it's time to graduate into the fascinating world of multi-stage water rocketry.
Using components that you are already familiar with, the Ozone Probe adds a very innovative interstage fill/release mechanism, a reduced upper-stage nozzle, and an enlarged lower-stage engine to create the functions of booster and sustainer. The booster accelerates the entire assembly to target velocity and then drops out of the ring and back to earth, freeing the sustainer. All the sustainer has to do is keep itself going upward. This it can do for a long, long time.
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