A three-day supply for one person is 3 gallons (12 liters) of water – one gallon (4 liters) per person per day. Also include an extra one gallon (4 liters) for a medium size pet. That one gallon should last three days, but plan for more or less if your pet is very large or very small.
1 day, 1 person = 1 gallon (or 128 ounces) = 7 – 20 ounce bottles = 4 liters
3 days, 1 person = 3 gallons (or 384 ounces) = 21 – 20 ounce bottles = 12 liters
During an emergency, you should drink at least two quarts (one half gallon/two liters) of water a day. Drink 3-4 quarts (3-4 liters) a day if you are in a hot climate, pregnant, sick, or a child. Some of the water in your emergency water supply will be used for cooking or washing.
If you buy commercially bottled water, it should be replaced once a year. Store your water in a cool, dark place to keep it tasting fresher longer.