With water rockets, you pretty much have 2 options. There’s either the ready-made reproduction retro toy called the "Water Powered Space Rocket", or you can make one yourself.

In 1953, the Water Powered Space Rocket was Toy of the Year according to House Beautiful magazine. Believe it or not, kids still go wild over it, and for good reason. Just fill the rocket with water, pump it a few times, and the pressure will propel it into space (okay, about 35 ft). The 6" tall hard plastic rocket is still sure to please, and even comes with instructions. This retro toy makes a great nostalgic gift or a fun science toy.

for $6.95

Going the DIY homemade route, you can create your own water bottle rocket or water rocket launcher. Make sure you take all safety measures into account and then learn how to build a water rocket. Now you can honestly tell your friends that your hobbies include "rocket science".