I have heard that if you drink a lot of water as a habit, the body doesn't do much retention.
Therefore, if you are preparing for a hiking in the desert where not much water will be available, is lowering the water intake a few days before the hike a better approach to deal with the situation by adapting gradually to the extreme conditions?
EDIT: Thanks for the great points and ideas.It would be nice to see some scientific research to learn about the optimal approach.