It's not just drinking water heavily, you need to combine it with very heavy sodium in the week prior to the shoot, and then when you cut out all the sodium 2 days prior, the water over the next day flushes out all the sodium in your body, and it will give you a dehydated look, as if you'd been drinking sea-water all week long. And then no/little water the day of to get the maximally dehydrated/veiny look, essentially going about 16+ hours on no water after a week of seawater and then 2 days of fresh water.Oh yeah, and I forgot the reason why I told that story - I was already holding very little water weight because of the low carb diet, but overnight I flushed out another kg of water weight.
Or so I've read, I'm obviously not a bodybuilder either.