As soon as disaster strikes, many folks would say you need to rush to the taps and start filling buckets, bottles, and even your bathtub with water--because you may not have pressure in the lines for long.
But what if it's too late? What if the water is no longer being pumped? What if you didn't have the forethought to stock water for you and your family ahead of time? What are you going to drink?
Fortunately, there's already a lot of drinkable water in your home, right now. It's in your water heater (unless you have a tankless heater).
The average home has a 40, 50 or even 75 gallon water heater in it. That's ten or more days of potable (drinkable) water for a family of four. And conveniently, your water heater has a drain at the bottom. And that drain spigot is threaded for a standard water hose.
Now, if you haven't flushed your water heater in a while, there may be a lot of silt in the bottom of the water heater--all the calcium and minerals that are in city water at any given moment, but which accumulate in a water heater over time.
There's also water in your house's pipes. Just turn off the water at the main valve, then open a spigot at the lowest point in the house and drain your pipes. That's quite a few gallons of potable tap water there as well.
The point is, when disaster strikes, you need water to survive--most people can't go more than three days without. But for short-term disaster scenarios, there is water in your home already, so don't panic.