HOLA amigos,
In light of recent tragedies in our deserts, perhaps this subject ought to be expounded on to more detail, for we have visitors who come to T-net just to read our discussions for information.
First - if you are in the desert and have NO water, DO NOT EAT. Eating food of any kind, makes your digestive tract draw water from your body to enable it to digest the food, so no matter how hungry, until you have water do NOT eat any food. You can live a long time without food, but only a few days without water.
The condensation method alluded to previously <known as a Solar Still> may seem mysterious to someone unfamiliar with it; the idea is to dig and expose some damp earth in a hole or hollow, place wet stones, fresh vegetation etc in the hole, place a container in the center to collect the moisture, cover the hole with a plastic or canvas tarp (plastic works much better) and weight it all around, plus one small stone in the center to form a depression there - the idea being that the condensation from the hole will collect on the plastic, run down to the center and drop into your container. It does work, even with toxic plant types - <
EDIT DON'T use TOXIC plant types, it WILL produce water but it may be toxic> - however if you are in a survival situation you must build several of these condensors for each one will only produce a little water each night. Here is a fair explanation with pictures
http://www.ehow.com/how_12584_make-solar-still.html
Finding water where there are NO plants is a tough proposition; look for dark earth, dark-colored stone, darker stains on rock. These may indicate moisture present, which by digging you might reach. If you decide to dig, try to find the lowest point in the dark earth to dig and be prepared to dig deep if necessary.
If there are plants, a big thing to learn is water indicator plants. I will get to this in a moment. If at all possible, look to find an actual water source. Trees are a fair indicator - few trees can survive where there is no water. Look for a darker green "streak" of vegetation in the canyons, or gullies, dry washes etc - sometimes even a dry creek will have a natural "tank" where the water collects and doesn't go dry when the creek does. If there are trees, sometimes you can find a hollow in a tree that is holding water. Most often water you find like this will be absolutely alive with little squiggly things and green algae, but after boiling twenty minutes it should be safe to drink. Plants in deserts tend to be fairly evenly spaced, but where there is water, the plants "crowd" in on it. Look for a patch of denser vegetation.
Now back to those indicator plants. Where you see this type of plant, you will know that water is close.
Cattails - water within three feet. This could be vertical feet OR horizontal or any combination, but it will be close.
Elderberry bush - water within ten feet. <ditto on direction>
Desert Hackberry - water within twelve feet (if memory serves, I welcome any corrections) also has orange edible berries
Sycamores, Cottonwoods and some types of Willow trees are good indicators of water, but the water may be deep in the ground.
Mexican Palo Verde, Button Bush, Pecans (wild) Bald Cypress and Salt Cedars all indicate water nearby, may be able to reach by digging.
As a general rule, in desert country - mountains are better than flats for finding springs or water tanks. The flats are MUCH more stingy with water sources, if you are in the situation and have to choose, head for the hills rather than striking out into a wide flat plain in the desert.
DON'T ration your water, you must drink at least a gallon a day - you will not lengthen your survival by rationing it.
Game trails often lead to water sources - if several trails seem to be leading into some particular place, it is a good place to check out for water. Flocks of birds may indicate where water can be found - watch for doves in particular, if they seem to flock to some spot to land, it may be a spring or water tank. They will often circle over waterholes in the early morning and late afternoon around sunset. Waterfowl would be even better of course, but you don't see a lot of them in the deserts.
Everyone knows about the good old lifesaver Barrel Cactus, an emergency source of water in the desert which has saved many an old prospectors life, but not everyone knows what it looks like.
Chopping into such a cactus (be careful about those spines!) will yield a nice somewhat syrupy drink, however you should be aware that it also has some 'astringent' properties, which may actually make you FEEL thirstier,<may make you feel nauseous> but it can save your life. DON'T eat the pulp either, just suck on the juices.
Do stay out of the Sun, and restrict your activities during the heat of the day - if possible, travel and do any work you must do in the early mornings and late evenings or even after dark if there is enough light to see to do so safely. Finding shade may be a big problem, but if you have a tent or tarp or anything to make a temporary Sun-shelter, it will do.
Do make sure to include enough SALT in your daily diet; your body needs it along with that water to regulate your body temperature and sweating uses up a surprising amount, so include some salt tabs in your pack.
Good luck and good hunting amigos, DO go out and explore our beautiful desert country, but educate yourself and do it smart - don't end up being a tragic statistic. There are some excellent desert survival books available, and some good info on the internet but some online articles are questionable so if you are relying on these sources, check the info against other sources before trusting it.
Oroblanco
The answer is really simple. 
But, hopefully, you won't get into this situation, because you have planned for emergencies, by bringing more than what you think you need - and drinking it - even though warm water is hard to drink, too - drink on a regular basis, even if you do not feel thirsty.
