Cold water slows down digestion so your food is only partially digested (stomach is at about 100 degrees optimally), and it makes the entire body cold so that it has to work harder to stay warm and keep the precious major organs warm.

Sports people, atheletes, will drink cold water during like, say, a marathon, because they've found that it is absorbed quicker thru the stomach lining.

Warm water, especially when drunk really fast, passes through the entire body quicker and induces cleansing such as peristaltic action in the colon, and the kidneys to flush.

So if you want to rehydrate with warm water rather than cleanse, best to have a bit of salt in your system or drink it very slowly.