Thanks for the comments BCguy
Mud,
Great question.
In SHTF of TEOTWAKI situations <snip, hack, cut>
finally, go online and find one of the water test kits and buy it and throw that in your BOB. You want one that let's you make several tests and get the results right on the spot (they are similar to what you use to test aquarium water for your fishies). Once you get to your TEOTWAKI location you can begin searching for and testing water sources to get your long term supply secured.
Okay, this is too long but you hit on a topic about which I'm passionate