Too much of a good thing can be bad. I often hike in deserts. I don't "tank up" much at water sources. If I am thirsty I drink until I am not. I don't think I can drink two liters at once -- that is 1/2 gallon of water! We need to keep our body water in equilibrium if possible. Too much or too little is bad.
I eat the foods I need for nutrition, not for retaining water. One change I make in hot weather is to eat salty foods -- not constantly, but enough to replace salts lost during perspiration.
When I need to carry more than 4 liters, I have two packs that both have two side water bottle pockets that each can hold a 64 ounce (2 liters) Gatorade bottles -- I ordered them this way specifically because I am in deserts a lot. Other water I carry in the pack up high and against my back.
If someone is going on a 10 day hike and will be carrying 5 liters of water, then they should, in my opinion, have a proper pack with a suspension that will transfer the weight to the hips -- this means a real frame. Of course with a properly fitted framed pack, there should be no (or little) weight on your shoulders.
If I were going into the desert for 10 days, I would for sure know what my pace would be, or have some very realistic bail out points or alternatives.