Fluid Temperature has No Effect on Hydration
We reach for a ice-cold beverages on a hot summer day to rehydrate ourselves in the sweltering sun. Frozen water bottles and ice coolers are used to avoid warm drinks, which seem to evaporate once they hit your mouth.
Contrary to the practice of cooling or warming liquids to relieve your thirst, this study shows that temperature has no actual effect on hydration. Fluids administered to infants at body temperature (37°C) versus room temperature (23°C) were equally effective at hydration. This was the same case in both rotating and bolus (all at once) oral rehydration methods.
However, colder fluids pass throgh your body quicker than warm fluids, giving the perception they are better for hydration. This is not necessarily the case. Additionally, your body experiences a temperature cooling when filled with a colder liquid which feels more refreshing on a hot day. However, when it comes to thirst, colder or warmer drinks will quench it just the same.
Pizarro, D. T., Posada, G. S., Levine, M. M., Nalin, D. R., & Mohls, E. V. (1987). Comparison of Efficacy of Oral Rehydration Fluids Administered at 37°C or 23°C. Journal of Tropical Pediatrics, 33(1), 48-51.