SouthWest Desert here: I carry a 100 oz camelback. I know some ppl don't like it having a pack on their back but I have 2 water bottle cages and a camelback on Any ride I"m doing in the heat..........I figure it's better to have TOO much water than to not have enough. I keep electrolyte drinks in my water bottles and carry extra packets in case I finish up the bottles and find a place I can refill. I keep plain water in my camelbak - which lives in the frig when I'm not riding. I'll also add salt to my electrolyte bottles since I use a sugar-free, sodium-free replacement drink. The hottest I've ridden in so far was 109 degrees....and I didn't have any problems. (course I also LOVE the heat!)