There is always a lot of questions about solar stills. Here is my thoughts on the solar still. I believe that solar stills need to be cut out of survival manuals because they are a waste of energy. Survival schools that are up to date no longer teach this method because they are time and energy intensive and the amount of water that they poduce does not make them worth the effort. Anytime that you conduct a survival maneuver, you need to determine whether it is worth the energy to conduct the effort. For example, it takes more energy to reach down and pick an edible mushroom than you will recover from it while consuming it, therefore, mushrooms are a negative energy gain. Solar stills are in the same category. To build a solar still, you pretty much have to exhaust all other methods of gathering to water to resort to digging down into the dirt far enough to make this thing work. The principal of the solar still is that moisture from the ground is drawn up and evaporated onto a clear plastic cover. First, for there to be enough water in the ground to do this, there is probably vegetation around that will produce the same amount of water through a simple evapotranspiration bag. Therefore, in a desert environment, the amount of energy that you will burn and the amount of water that you will sweat making this still will outweigh the amount of water you will gather from the still, making it a negative energy drain. If you need to prove this to yourself, build one, wait for the water, then drink it when it comes and see if your thirst is quenched. OK, so build seveal and go to each one throughout the day. Same thing, a solar still hole will only produce for about two to three days at the most, having several means that every three days at the best, you need to re-dig the holes. Still an energy drain. You would be more productive using a evapotranspiration bag, or a sponge on dew laden grass, but that is another thread!