If you drink two litres of water and eat 1 kilo of meat the chances are you will have had a number of toilet breaks during the meal so will likely weigh just over an extra kilo unless you were dehydrated to start with.
Manipulating water intake is a good way of fudging weight for competitions, like boxing and powerlifting. I have used it on both and managed to be in the weight class I wanted each time, though strictly speaking I shouldn't have been. I never felt guilty about this know the other person punching me was the same weight or more.
