This post has a water themed Birthday party including this relay: The first kid starts with a full cup of water, then pours it over his head and the second kid catches it and repeats and they keep doing this to see who can fill up a jar the fastest.
Roll Out the Marble Game. Need cardboard tubes & a marble. Form a line & pass the marble. After the marble leaves your tube, move to the end of the line. If you drop the marble, you're out. For large groups, make teams. pre-meeting activity or group game