It's a lot cheaper doing it that way than buying it by the gallon bottle.
We have several WalMart 5 gallon frosting buckets ($2 each from the bakery) filled with tap water in the basement. It can be used for flushing, washing, or even drinking/cooking. We also keep a few dozen 1/2 gallon apple juice bottles we washed and filled with tap water for drinking. That suffices for our panic/emergency needs, and then we fall back on the bucket based water filter and a local pond.
Why wait until an emergency to pay big bucks for bottled emergency water when it is free right now with just a bit of foresight?
The frosting buckets are a good idea. Mr. GG2 has made friends with the ladies in the bakery at Ingles and they sell him the bucket for about $1 I think. Way cheaper than buying them at Lowes.