I really think that by "water game", we really mean a liquid game. Some sort of non-conductive fluid like mineral oil could be a possibility (though probably not because it would be very messy).
Water is a possibility, though, because you can get some anti-conductive agents (with anti-corrosives built in). A couple drops of these inside a pool will make sure the water is non-conductive. These are the types of liquids that you would use if you were water cooling your PC (not regular liquid cooling). However, these liquids can get quite pricey, and if the cheaper ones are used, a safety hazard.
Your claim that it would be hard to build a pool in every stadium is partially true. FIRST would actually use some sort of a pop-up setup, kind of like those folding pools you get. These fields are foldable. FIRST only makes a certain number of these fields, which they transport around to the events. Remember that not every event happens at the same time.
For the 2013 game, Ultimate Ascent (as all of you know it by), the volunteer team set up the field before you arrived and dismantled it after you left. The field is modular, so it easily comes apart and folds up, making the transportation a no-brainer.
The water could be transported around with the field. An oil-tanker like truck could haul the water between the competitions.
However, it would be very impractical to do a water game because of all the problems the teams would face getting the setup complete. For those interested in water games, try the
NURC (National Underwater Robotics Competition).
By the way, Mr Forbes, or anyone from 1726 or 842, where can I watch the kickoff (or whatever their opening ceremony is called)? I want to see what the game is!
