You take clean water for granted, and when apocalyptic fire sweeps across the continent, you'll quickly learn what much of the world already knows: Water purification is life.
Sure, you might get by on secret watercooler stashes and allegiance to a water baron or two, but there will come a time when the only available drink is questionable at best. You'll want to purify that stuff before you ingest a bellyful of pathogens or chemical poisons.
If you run across a CamelBak All Clear UV water purification system (or something similar) amid the rubble of your lost civilization, add that puppy to your gear. This $100 bottle uses a built-in, battery-powered ultraviolet light to kill waterborne bacteria, viruses and protozoa in 80 seconds flat [source: LaBarre]. Other on-the-go water filters such as the LifeStraw instantly turn a questionable puddle into a potable mouthful.
When all the CamelBaks and LifeStraws are gone, however, there are still ways to ensure your water won't kill you. Boiling will kill most types of disease-causing organisms. And if the water appears murky, you can strain it through a cloth or allow it to settle and skim from the top. You can also use a barrel with several feet of sand in the middle to filter collected rain into potable drinking water [source: Green].
Or, buy it from your local wasteland warlord with your undying service. Look, we can't tell you how to live your post-apocalyptic life.