i toured across southern utah last august, most days the tempeture was between 95 and 110. i carried 2 buke water bottles(20 ounces each i think) 80 ounce camel back. i bought one of the small 6 packer colapsable coolers and would have a quart of gatorade and 2 quarts of water in there with ice. i can't tell you how nice a cold drink can be so it was more than worth the wieght. i tried to make sure i took a drink about every ten minutes. i'd drink what was in the camelback, then refill it with the cold water in my cooler, and drink the gatorade when i stopped for breaks. only once came close to running out of water on a particually long slow day with no services.
i was on a pretty lightly traveled route but basically every day a few people in cars would slow down beside me and ask how i was and if i needed anything, so water never became an issue.
one thing i would do is make sure you know how far it is between services. i move pretty slow and would have liked to have found a store about every 30 miles or so, just to get a cold drink, and maybe find some shade to take a break in for a few minutes. it was a great trip but that would have made things nicer.
if you have any other questions feel free to PM me.
any ideas where you plan to tour? i love that part of the country and theres a lot of neat stuff to see.
my tour started in st. george, utah and went thru zion, bryce canyon, capitol reef, glen canyon(may have name wrong need to check my map. cap reef to glen was particularly rough, deceptive and long, only stretch i had trouble with. then headed to alb, new mexico. if i were to do it again i'd go a different route from cap reef to new mexico.
anyway have a great time and PM me if you have any questions or post here .