Should you find yourself in a post apocalyptic wasteland ruled by water-hording warlords, please remember the solar still.

One of the most significant survival tools created in the last 40 years, the solar still was developed by two physicians working for the U.S. Department of Agriculture. Results of extensive testing in the Arizona deserts by the U.S. Air Force proved that when properly assembled, the still can save your life.
…
There are only 2 essential components to constructing the solar still — a container to catch the water and a 6 x 6-footsheet of clear plastic. A shovel or trowel, a length of plastic tube and tape are all optional.
The container can be a collapsible cup, an empty plastic bottle, a small cooking pot or just about anything with a large enough opening to catch falling drops of water. In a pinch, even tin foil or a sandwich bag can be fashioned into a workable receptacle.
The sheet of clear plastic can be a ground cloth used under tents when backpacking or a thin painting drop cloth. Both work well as long as there are no tears or holes. This is the one item that should be carried at all times, since there is no natural substitute out in the boonies. I keep a 6 x 12-foot plastic drop cloth taped inside my daypack, large enough to make two stills if necessary. Some desert rats like to keep their plastic sheets folded inside a hip sack or as part of their first-aid kits.
A 6-foot length of flexible plastic tubing, similar to the kind used in fish tanks is a non-essential but desirable addition to the still components. This will allow you to drink accumulated water without needing to break down the solar still, inevitably affecting its efficiency.