There are filters, and there are FILTERS. Some are cheap yet good enough for occasional camping or backpacking, some are expensive, sturdy, and made for long term usage. http://www.katadyn.com/en/katadyn-products/products/katadynshopconnect/katadyn-wasserfilter-endurance-series-produkte/katadyn-pocket/
http://www.berkeyfilters.com/berkeytech.htm
There are other things that can be done to pretreat ground water to make these even more effective- filter ground water through a bed of sand/gravel/charcoal to remove particulates and turbulance (even radioactivity). before using the unit for final filtration.
How long can you survive on $250 worth of bottled water?
I know a man who runs mission trips abroad, to places where the same river serves double duty as sewer drain and water supply. He tells me he's tried filters in the past (good filters, Sweetwaters and Berkeys) to treat water for his groups, and each time someone got sick. The problem is viruses. Even the best filters leave enough virus in the water that people can still get sick from it. Yes, even the Berkey.
He says bottled water is best, boiled is second best, and chem treated is third. He's given up on trying to find a filter that works. I take him at his word, he knows this stuff pretty well. Listening to him about how "modern primitive" communities live is quite enlightening.
It's worth noting that the water found in the wilderness here in the States is generally pretty clean. The only contaminants to worry about are giardia or cryptosporidia, which any average filter can handle with ease. Heck, thru hikers often drink right out of the stream, and they usually fair well well enough. If your plans are to hide in the hills until the mess blows over, then a filter is probably OK. Just make sure nobody else is crapping in your stream.
I figure boiling is impractical in a prolonged emergency. The amount of fuel required would be prohibitive. And even if you had the fuel you'd probably be better off saving it for some other purpose.
Chem treatment probably works. I don't relish the idea if drinking bleach with my water, but in a pinch I could make do.
That leaves bottled water. If you're careful what you buy you can get cases of 35 half liter bottles for about $3.00. A case is enough for about a week for one person, if you only use it for drinking and rely on something else for washing and sanitation. For $250 I could buy 80 cases, which would last 10 months for my wife and me. That's more than I feel we need.
YMMV. I figure in the end, the only real solution is acreage and a hand-powered well pump.
