Here is how the "average" urbanized person thinks. They think of how many bottled waters they drink in a month. Since they hardly drink bottled water, they reckon a few bottles will be sufficient.
This sounds crazy but I guarantee you many think like this.
I had a buddy who said all he needs is to have enough rechargeable batteries for his iPhone and iPad and he can watch movies, communicate for help, etc. during his catastrophe (he is on the East coast).
I said, your router and Internet link might be down and the cell towers also need power.
He was shocked, never even thought about that.
He also said he just needed a water filter, not needed to store water.
I said, where are you going to get the water to filter? You going to head down to the sewers?
He couldn't understand why I asked that. He said, why can't I filter the water from the tap? It's just going to be undrinkable, but I can filter it right?
I told him the water pumps work on electrical power. He was floored.
Note that the above conversation took place AFTER all the chaos of Superstorm Sandy.
He works for a major bank, not that it has anything to do with it (probably). LOL!