Water pistols are fabulous. And there is excellent coverage in telling folks how to get wet.
Terrific water guns are available both at discounters like Wal-Mart and at advanced specialty stores. You can expect great design and good throw and soak ratios. And If you truly want to get folks damp, there are dual action hand pumps that throw a 3" stream of water about 20 feet. Nail the kids with that and watch them view you with new respect.
Water pistols are safe. They keep folks cool. They're fun. And running around nailing the neighbors is great exercise.
Kids like them too. Even video-game hardened adolescents, who would never be caught dead even talking to you, can't resist the onslaught of the Buzz Bee Blazer 2005.