Well, my buddy who worked at a phys therapy hospital said that even the tank of water method is still only accurate to +/- 5%, because the water displacement is also determined by how much air is in your body. You CANNOT expel all the air in your lungs, and then there is also air throughout your body, and in your gastral-intestinal tract (hence the farts and burps). So, even testing at 2% in the tank, he still could be higher.
-j69