Originally Posted by LtBrett
The mythbusters or some other tv show tested the drain water vs. leave it in question. The clear winner was the cooler with the ice and water. Think about it in terms of the overall cold mass being reduced by draining out the water. Obviously, you want more cold mass than less.
^correct. Water is a liquid. It will both heat up and cool down slower than air (a gas). The melted ice in your cooler will be warmer than the unmelted ice, but cooler than the surrounding air. Long story short -leave the water.
As for urine... your surrounding body is mostly liquid (er.. some gas, I suppose). I'm not an MD, but I doubt emptying your urine filled bladder will leave you with a gas filled one... just a collapsed empty one, surrounded by mostly body temperature water. But... the urine will add some liquid mass to you, and it should hold heat. I would imagine the effect is minimal, though. I weigh 170lbs, and piss at most a pint at a time.