I also find that it's helpful in HOT weather... to carry COLD water.

My Camelbac is an excellent insulator. I fill it up with ice and water... and it stays cool for hours. It's amazing!

I also have an insulated water bottle. It works pretty good. I try to drink that first though, as it cools off quicker.

During the summer I ride in humidity and 95-100F weather. I haven't had any issues yet. I just make sure that I drink and drink.