Split teams up with at least 4 people per team. Using two large bed sheets or blankets (one per team), have the teammates hold the sheet on corners, etc. Starting with one water balloon, launch the balloon over to the other team. The team must catch it in the blanket and not let it burst. If they are successful they get a point. As the other team launches the balloon back over to your team, have your teammates loosen up their grip on the sheet so the balloon doesn't bounce off. As the game goes on, add more balloons for competition.