Well, first of all, try using the several gallons of water in the reservoir tank of the toilet if there is ever a water shortage (the squarish thing at your back when you sit down on the seat not the bowl).
It’s fresh and clean enough to drink, unless you’re a little squeamish about drinking out of any part of a toilet. Why should you be? Your dog probably does it all the time. If so, you can purify the water with a tiny amount of bleach.
First the warnings: Undiluted bleach is poisonous, and should not be drunk, or spilled on your skin or eyes, and its fumes should not be inhaled for any significant amount of time.
Only bleach labeled “liquid chlorine bleach” should be used. It should be 5.25 percent hypochlorite, read the label carefully, and should not have scent or other cleaning agents added to it.
Follow these mixing guidelines to purify water in an emergency: For every gallon of clear water, add 8 drops of liquid chlorine bleach. For cloudy water from more dubious sources, double that amount to 16 drops.
Stir the mixture, leave it in an open container, and wait for at least half an hour before drinking so most of the bleach can evaporate off.
Keep in mind that bleach will kill many of the pathogens that can make you sick, but it will not neutralize chemical poisons or pollutants.