Solar stills

Composed of little more than a thin impermeable membrane, a length of tubing and a collapsible bucket, a solar still is one of the simplest machines. Essential for long term survival in the open waste as a potable water generator. They can be made of any size, though there is a minimum effective diameter to produce enough water to survive on.
To deploy a solar still, the first step is to find a source of moisture. Either by finding a patch of damp sand, materials containing moisture or contaminated fluids which contain water. Next dig a hole slightly smaller than the diameter of the membrane preferably with sloping sides and deep enough to place the collection vessel below the weighted membrane. Place the bucket in the bottom, and put one end of the tubing in the bottom of the bucket. Use a weight to hold the end of the tube down. Lay on the ground so the other end will be beyond the membrane and take steps to keep it clean. If you are distilling from a source other than the ground itself, lay those materials around the catch bucket. Finally, place the membrane on the ground, covering the hole completely. Seal the edges with backfill and place a small weight on the membrane over the bucket.
Heat will cause the water to evaporate, it will be cooler on the surface of the membrane than the air temperature of the hole. Water will condense on the underside of the membrane, and drip into the bucket. The tubing can be used to extract liquid water without disturbing the setup.
Production will vary depending on many factors. Some experienced wanderers will sleep in thier still and so collect the condensate of their own sweat as well. Best results are from larger diameter membranes, wetter ground and from harvesting moisture collecting plants.
Care does need to be taken with the membrane as any holes or failure to completely seal the edges will result in loss of heat below the membrane and loss of evaporate.
Alternative setups are possible. Particularly enterprising people will spread several stills over the ground just before sunrise to catch the moisture from the overnight microfrost. Or possibly rake that top layer of sand into a larger prepared hole to extract that water the moment it gets warm enough.