Rinky - that's why you need activated carbon and sand. Layer those in the bottom of one of the drums, poke some holes in the bottom, use the other drums to feed and collect, and you have pretty clean water.

frontier - just make sure you keep enough gas onhand to get to your hide out, obviously. If the power goes, no more pumping gas.

Ron ap Rhys - camping filters are only good for around 50 - 200 gallons for each filter, depending on size, brand, etc. That is why I keep several back-up filters. And I do the same thing with my camping food.