If the highs are in the 60's or maybe low 70's I can easily get by with 1/2 gallon per day, but I am not cooking (there is a little bit of balancing -- non-cooked food can be heavier). Also remember I have been living and hiking in the lower desert for well over 30 years, and have acclimated somewhat. Wisner and I did a hike last year and at the end of the first day I had only consumed a little over a liter.
If I find a spring (usually unreliable till you find water), then I can adjust and sometimes adjust my route to make a loop(s) back or even cache some water after filling up at the spring and dump some of it.
Last December I did a trip and went 2 days between each water re-supply, with a 64oz Gatorade bottle in each of my side pockets, the gallon carried extremely well in the LBP, and I had a Mountain House dinner each night, oatmeal & coffee for each breakfast. Desert hiking in the spring, fall and winter I can stretch 3 gallons over 6 days, and each day the pack gets about 5 or 6 lbs lighter with food and water consumption. So for a 6 day trip we are looking about 31 - 33 lbs of food and water (picked 6 days because it was easier to calculate in my feeble mind). Add all the gear and it is pretty easy to get in under 40lbs total. By day 3 the total pack weight is around 25 lbs or less. The alternative is not taking the trip I want, or hiring a Sherpa, or buying a burro. I don't think any Sherpas live in the lower desert, and I know diddly about pack animals -- other than wild horses and burros often foul water sources and leave road apples (non-edible) all over the place :)
Oh, and did I mention I will probably not have to share the experience with anyone else except for a few coyotes, rattlesnakes, and hopefully a big horn or two? And even rarer, I get to see one of these once in a while.
or acres of these too thick to walk through