I would point out that there are many sources of water that can be made available in an emergency sitiation.  Understand that if you are on the trail long enough, you eventually will have to rely on a water source of some sort.  If it is not there, then you may have to improvise.  Look up Water Stills, and Condensation Collection as examples of alternate means.  Obviously we want to LNT as much as possible, so a Water Still should be (IMNSHO) a last resort as you have to disturb so much soil. 

That said, I'm usually willing to hump an extra "just in case" litre of water with me on most trips.  Doesn't help with the original post, but it is a case of risk management/assessment, and worth considering based on the local 

Hope this helps!