Boy Scout motto is "Be prepared."

They should prob. lay off the pot, amirit?

***
I really don't know much about this. These are all chemistry questions, and not really the kind of stuff I focus on.

***
Best thing would probably be to control a plot of land with adequate ground water, dig a well, and protect that land and well from thieves.

You can purify water by boiling it, which will kill any viruses or bacteria in the water. This wont make the water taste any better, and it wont remove non-biological threats. I believe this is what the chlorine does, i.e. kills biological threats, but not other chemical impurities.

If you up your game a bit and don't drink the boiled water, but rather you use the boiling to evaporate the water, then condense the evaporate and drink that... then you have distilled drinking water. This will be much improved in taste, having separated out sediments and other contaminates from the source water and the distillate.

If you're very careful, you can pass the water through multiple distillation steps at increasing temperatures in each step. This can separate any chemicals with lower or higher boiling points from the water. You only drink the liquid which boiled at the appropriate temperature. I.e. alcohol boils at a lower temp than water. So you can slowly raise the temp of a water/alcohol mixture to a temp where the alcohol evaporates, but the water doesn't. (There will always be a bit of water in there, due to the statistical nature of temp.) Ideally, you started with a water/alcohol mix, and ended with water separate from alcohol. If there is then some other chemical in the water with a higher boiling point, then you distill off the water, leaving that other chemical behind.


All of this is what I remember from purifying lake water as a boy scout and my middle-school chemistry class.

As to sources or methods of acquiring CaCl2, I'm totally ignorant, but maybe Chemist will show up and help you out.