We would make home made water rockets at work when there was nothing to do. We would use half liter water bottles, and a piece of steel brake line with a gas valve. We would drill a hole just under 5/16 dia. in the cap. Half fill it with water and attach it to air. We had about 150psi air system, and they were crazy to shoot.. (the new bottles are too flimsy). One of my co workers decided to try a Gatorade bottle, but the hole was drilled too small. It stuck and wouldn't come off the tube. The bottle blew up next to my head. I remember saying "I can't feel my hand and my ears are ringing.. My hand was numb and i couldn't hear for about 5 minutes.. yet we were laughing like school kids... We grew up in a different era... If you weren't dead, it was automatically funny........... When i was about 14, we made a rocket from leftover estes parts, and replaced the chute with FFFF. "Still can't talk about that one at Mom's house..