Yes, join the club. I am also from Phoenix and it is already over 100F. Bring as much water as you need. I usually take one standard bottle per every 10 miles and I usually do not drink too much because of a small body weight. But definitely take salt! Salt tablets may be very helpful I discovered Clif Bar Shot blocks: http://www.clifbar.com/eat/shot_blok.cfm?location=shot
They are outstanding! And they really taste good. Try them out as well.