Soakermedia has a really impressive water balloon launcher made from PVC – “Want to shoot an object at 140 MPH over 500ft? Then this launcher is for you! This article will teach you how to build one of the cheapest, easiest, and most powerful water balloon launchers ever invented. The launcher will shoot anything from a golf ball to a tennis ball at extremely high speed and extremely far. For wadding, a tennis ball can works best. For the valve, use a solenoid or metal ball valve at least 1 1/4″ in size.” [via] – Link & video.