During Coast Guard training in the 80s, we were taught that in a survival at sea situation not to drink for the first 24 hours. The reasoning was that it takes this long for the body to adjust to the deprivation and start conserving water, rather than passing it though. Once in the bladder, I don't think the body will reabsorb, but I'm not a medical expert.

It is also possible (likely?) that that is now old advice.