Car Wash
Although it may seem like drudgery to most adults, washing a car by hand appeals to many kids as a fun "grown-up" activity. Use an official camp vehicle or ask a volunteer to allow kids to wash a personal vehicle (just don't expect it to get very clean, especially if the participants are young). Provide several buckets filled with water, sponges and hoses connected to water sources. For the purposes of this activity, soap is not recommended. Let the kids take turns manning the hose while the others wet down the car and themselves. Make sure those in charge of the hose do not squirt others in the face! By the time they finish, they will probably be wetter than the car.
Sprinkler Freeze Tag
Set up several sprinklers in a large play area such as a field. Use a variety of sprinklers if possible, then arrange them in a way that the sprayed water will cover most of the play area. Have kids play a traditional game of freeze tag, in which one kid (or more) designated as "it" tries to tap other kids who are not "it." Those tagged have to freeze or stand as still as possible, until tagged by another player who is not "it." Those who are frozen will be getting hit with water from the sprinklers as they stand still, unable to move away.
Water Balloon Toss
The traditional water balloon toss involves pairs of kids throwing water balloons back and forth. They begin by standing close, about a yard apart, facing one another. After every successful catch, each takes a step back, so that they have to throw the balloon further each time. Ideally, balloons should be small and tightly filled so that they break fairly easily when dropped or caught too roughly. To make the game more challenging, older kids may want to run while throwing, football-style.
Disappearing "Water Ink"
Since summer heat causes water to evaporate quickly, kids can use water to write or paint just about anything and watch their work quickly vanish. Provide kids with buckets of water and various-size paint brushes. Encourage them to paint messages or images on any available outdoor surface, such as sidewalks, buildings or concrete floors. Older kids may want to use the game to play "spy," writing secret messages that others must decipher before the water evaporates.