I really prefer water at air temperature, but when it gets super hot and my ability to cool myself by sweating is maxed out, I know that drinking cool water helps me keep my core temperature down.

If I fill my Platypus (neoprene insulated) with ice cubes, then top it off with water (which comes from my tap at 55°F), it'll stay quite cool for as long as it takes me to drink the 1.8 liters. I save the frame mounted bottles for electrolyte drink, mixed extra strong.