Our training group in So. Ga. goes by the "rule of 120": combined water and ambient (air) temp of 120 degrees. Sunny day at 70 and water at 50-plus okay because how dogs feel after exiting water and drying out on a nice day with sun is important (my opinion).
Very important to keep in mind, even on older dogs when temps are lower...Steve S
"Your dog learns as much by doing his work right,by your praise and encouragement, as he does by your displeasure and correction." DLWalters