The warm water / cold water thing is one of those things that I've heard a thousand times and seen zero scientific evidence of it being true.
If my body absorbed water in a significant way, shouldn't I not have to drink any if I swam all day in it? Dehydration at sea? Go for a swim!
Child, please. I'm not a freakin amoeba. Osmosis is something that we have sucked at since evolution took over. Next time the first epidermal layer of my skin gets lead poisoning, I'll be sure to immediately post on NES about how wrong I am.
But until I see some science, I'll use luke warm water so I don't look like a featherless goose washing my freakin hands.