I rode the Western Express from Cedar City UT to Dolores CO in June 2009. Streams hadn't dried up yet so filtering was still possible, but I was able to buy and carry enough since I had an MSR 10 L Dromedary bladder. The names of the creeks like Poison Spring etc were kinda off-putting for filtering. There was piped water at the Hite Rec Area (Glen Canyon). Get ready for some unbelievably steep grades and some wonderful scenery!