Good point dude. When I said a few ice cubes though, I didn't mean enough to make the water really cold...just cool. I personally have been doing this for several years now and have had no ill effects but this is, however, not to say this would not affect anyone else so you're safe bet would be to leave the ice out of the hydration unit completely. I do stand on the Camelbak-style hydration unit though as it's also a good "almost" hands-free and out-of-the-way unit for hydrating yourself out on the field.Drinking water that is cold could give you stomach problems as well. During intense airsoft it is better to drink water that is Luke warm instead of chilled.
Thanks for the "safety tip" NL_Lexxie.