This is a broad question for me to try and get a feeler...
In the USA, what would be the maximum distance, anywhere, that one would walk where you would or could, not find a natural or human-induced water supply, if you were to do, say a Desert crossing? To make it easier, what is the longest distance you have walked or heard of US walkers/adventurers doing?
In the definition of water supply, go as far as including dodgy semi-permanent soaks/springs, and water supplies that require treatment by normal means (up to and including a really top line filter system like a Katadyn Pocket).
One day, when I get enough time, I want to work the remotest position in Australia from water. It will likely require alot of work though (alot of digitising of 1:250k topographic map features...once thats done its a relatively easy GIS procedure), and I'm guessing will be somewhere in either the Simpson, Great Victoria, Great Sandy, or Tirari Deserts, and will likely be in the range of 200-600km from any marked water source.