In water wars, there is really no place for diplomacy. There is only shock and awe. And now is the time for hell-raining-from-the-sky revenge (or a definitive pre-emptive strike)! Besides, in the arsenal of water-fueled weaponry nothing says SCUD missile like a "funnelator."
A staple for college frat boys for decades, funnelators are easily made at home and, best yet, light and easy to transport. In its most pedestrian terms, a funnelator is a three-person sling shot (there are one-man funnelators as well, but those have limited range; the three-person version can pierce a window or shatter a nose from a distance of, oh, 100 yards!). A Tom Sawyer version of medieval weaponry, in recent years funnelators have gone mainstream at sport events like Blazer games, where cheerleaders rocket T-shirts into the crowd.
To build, take 20-30 feet of surgical tubing (available at medical supply stores). Double the tubing over. Slide a piece of fabric--a T-shirt or old rag works fine--over the tubing and situate in the middle. This is your cradle.
Have your two tallest friends hold either end of the tubing; they are your "posts." Place a balloon in the funnelator's cradle and draw the tubing back as far as it stretches. To adjust your trajectory, change the height you are launching from. For longer distance (but less direct velocity upon impact), release the balloon from a crouching position. For less distance but more wham-bam impact, launch the balloon from a height level with the "posts."
The balloon will travel more than 100 miles per hour and is capable of serious damage--i.e., dented cars, shattered windows, broken noses. Use accordingly. PB