True on the filters, but for "normal" emergency situations one and a spare would be fine. That's roughly 2x the necessary supply of water/person at a gallon, so if it's just two, one could potentially last for 100 days. Even in our situation (1 dog, 7 cats for my wife, 3 snakes, and a gerbil) that'd easily last us through even a NOLA-type event, which really isn't likely in central Ohio.

But if I ever got truly survivalist nutty type, I'd need to get more. Not that have anything against the survivo-nuts, but I haven't crossed that line. I can see it in the distance, but I know I probably won't get there...