last summer I rode in North Carolina and at the hottest part of the day I was having to stop every 15 miles for water. Under those conditions I felt like an idiot for not having a hydration pack. I rode with one on my recent 600k attempts, and it's definitely something that takes some getting used to. My second try was more successful than the first. Under very hot conditions, load the pack up with ice and when done drinking, blow the water in the tube back into the pack or you will always be drinking hot water. If it's not too hot, I can make it almost 100 miles on 2 liters