Build your own water rocket launcher

We feel like the days when you want to play in the water are far behind us. But if you can still find a warm afternoon here or there this water rocket launcher build is a fun undertaking. We figure most of the time spent on the project will be in shopping for the parts. They’re all quite common, and once you have them on hand it can be assembled in under an hour.

The concept is simple, but that doesn’t stop people from building rather complicated water rocket rigs. This one which [Lou] devised is rather simple but it does offer connections to a hose and air compressor (the alternative being to fill the bottle with water ahead of time and use a bike pump for air pressure). PVC is used to connect the two inputs to the bottle via a pair of valves. The bottle is held in place while water and air are applied. The launch happens when a pull on that rope  releases the bottle.

Check out the build process and bottle launch after the break. We think that rocket needs a few fins.

16 thoughts on “Build your own water rocket launcher

  1. I loved this in school. I found that my best design used a PVC pipe outside the bottle as well, try not to make it looks like a potato launcher though.

  2. I have a water rocket launcher in my garage collecting dust, never had a good source for air when I built it years ago. But now with my new career path I have access to nitrogen!!! and of course pressure regulators… this might be more fun. If i recall correctly the typical bottle bursts at 140 psi..

  3. Clever design, I like it. I remember making water rockets with my dad when I was a kid; our launcher was just a simple setup that required filling the bottles by hand, but we had a lot of fun with it. :)

  4. You can purchase a schrader valve fitting with a threaded end to fit into the air portion of the pipe. I know, I use one for my water gun!

  5. von Braun got started the same way! It seems to go high enough with just water pressure for a fun project with the kids, maybe V1 and add the compressor for V2.

    1. And compressed air Is the propellant, high pressure water isn’t much use here, I found they went best when less than a quarter full of water!

      1. Have you tried soap bubbles? Fill is 1/4 to 1/3 full of water with dish soap and shake it up first.

        I want to try an electrolysis rocket. Have a pair of contacts touching the water (with a catalyst like soap) apply voltage until a few inches of water have been displaced with hydrogen and oxygen (in a perfect stoichiometric ratio) and then hit it with a spark. It would probably just destroy the bottle, but still worth a shot.

  6. PSI ratings of PVC usually exceed that of the 2-liter bottle you have connected. Coca-cola claims their 2-liters can withstand 150 psi. This may be true when the produce and fill them, but my experience has shown that they burst at about 120 psi after they’ve been handled and refilled a couple times.

    In short, your bottle should burst before your PVC.

  7. I wonder what would happen with an actual nozzle on the bottle… Take an air fitting like the one used here and cement it to the opening of the bottle (or the cap), and a coupler. Insert bottle into coupler, fill bottle, release the coupler, shoooooom….

  8. I built a small rig similar to (http://www.sciencetoymaker.org/waterRocket/buildWaterRocketLauncher.htm) this, using a ring of zipties zip tied to a pipe to grip the end of the bottle with an o-ring on the bottom (made from some vulcanizing tape that was laying around) to seal it. Instead of a pipe piece as in the link, I used the top of a gatoraid bottle (fit just right) and a leftover pipe from some type of baby toy (too destroyed to tell what it was) for the center pipe. Loading was with a valve from a popped bike tire cut out and shoved into a hole in the pipe (the leftover rubber hanging on the inside sealed as it pressurized). Some string/tape/sticks to keep it steady and done. It wasn’t the best, but it worked and used only fairly typical stuff ($0 in my case, probably <$5 if buying the parts dumpsers aren't full of anyway like the o-ring).

    1. NASA had plans for parents and teachers to build a compressed air soda bottle water rocket a few years ago. I made it for very little $ and launched it with my nieces multiple times using a car 12v tire inflator. Kids at a camp I worked at decorated 2L bottles with fins and cone noses that really improved the bottle flights.

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