Wet 'n Wild is a fun game on a hot day. It can be run in a number of ways depending on how many water troughs you can get your hands on and how many buckets the same size. A single large water trough or even a wading pool will do for part of the game. Then multiple buckets or containers the same size and some mixing bowls that are all the same size.
I'll write this up around a wading pool and set it up as a multiple team event. I'll even try and design it around my standard track layout I use in several other examples.
This is a rider passenger game, and it is usually run with a fixed time limit of two minutes per heat. Each rider and passenger and passenger starts in the safety area at the end of the track near the buckets shown in the diagram. Both teams are given a large shallow mixing bowl. The passenger must ride astraddle the passenger seat of the motorcycle while holding the bowl on top of their head. When the officials yells start and starts the clock the rider drives to the safety area at the other end of the track where they must stop to let the passenger dismount.
While the passenger is off the bike the rider must turn the bike around and point it back toward the other end of the field. At this time the passenger runs to the wading pool and dips the bowl into the pool to fill it with water. Then they get back on the motorcycle behind the rider and place the bowl back on top of their head. The passenger must be seated across the seat of the motorcycle and the bowl must be held on top of their head before the rider drives the motorcycle out of the mount and dismount area. When the team gets back to the end of the field where the buckets are located the rider must stop and allow the passenger to dismount. Then while the passenger runs over and dumps the remaining water in the bowl in the bucket on their side of the field the rider again get the bike turned around and pointed the other way. Again the passenger remounts and places the bowl on top of their head. They repeat the process until the official calls time. At the end of the heat the team with the highest water level wins.
Because of the amount of time involved if you have a lot of teams wanting to ride you might want to consider the amount of space you have available. If you have the buckets, bowls, wading pools, and space available it might be to your advantage to setup multiple tracks and run more than two competing teams at a time.
For safety sake you might consider a rule that the rider must turn around within their own lane at each end of the track.
For a little added fun, if you have hay bales around your track for safety you might consider putting the wading pool or water trough on the other side of the hay bales and making the passenger climb over them to fill their bowl.