there's not a lot of medical ground for that.
you see, alcohol travels in the blood. the way the body gets rid of it is:
- by metabolising it in the liver
- by excreting it in your urine, breath, sweat
so in theory, drinking 2L of water will cause you to urinate more and excrete more alcohol. in theory sweating a lot could also cause some alcohol to be excreted....
...but the reality is that the amount that you would lose is pretty insignificant and the main determinant of how your body gets rid of alcohol is the metabolic capacity of your liver.
BAC tests measure the amount of alcohol excreted in your breath (in your lungs, the blood travels very close to the air (<0.05um), exchanging many things with it). drinking 2L of water has NO direct masking effect on the way the test measures your BAC
cheers,
Warren