It's a useful reserve for potable water. If you have nuclear fallout coming down, it's not a given that you can trust the tap water to be clean, if it runs at all.
Probably to quickly stock up on drinking water.
Stocking up on drinking water or having a source of water to flush the toilet with (by manually refilling the tank).
Drinking water. Don't flush the toilet because you might eventually need the water in the tank too.
I've never understood this. What do you do when you need to defecate?
Poo in a bucket, put a lid on it. If the alternative is eventually dying of thirst or having to venture out into a contaminated neighbourhood, necessity compels.
FYI like 90% of your comments are flagged dead, but I read through them and think they're hilarious. You might want to create a new account.
Having a reserve of potable water.
Because the fallout would poison the water with radioactivity