By 2020, the state of the world's water supply is projected to be pretty stark, and this is likely to spur conflicts between several countries. I propose that World Water Day should address this... perhaps in a game!
I propose a live-action game in which each participant is given water "points" which represent all the water they may use for the day. These are determined randomly, along with assignment of an associated country. They log their activities to "use" the water points they've acc**ulated, representing their use of water, which they agree to limit for the day to what is possible using their points.
Players can locate others via a gps map, and may virtually fight to steal one another's water, if they are close enough. From time to time during the day, real locations are highlighted as refresh points. Anyone going there may stock up on virtual water (and naturally "fight" others for access to their virtual water). Real watergun fights are also encouraged at these locations to gain water.