FWIW, insulated Polar and Camelback bottles filled with ice and then water (or "drink") will keep the water cool for about two hours in 80s or higher. Beyond that time, and @
honcho indicates, the liquid warms up. However, since my bikes have space for two bottles, and I need to drink at least one large bottle per hour at those temperatures, at the end of two hours they're empty (which is worse than warm!), so I'll find a place to refill them at that time.