The minimum amount of water to store is one gallon a day per person for two weeks (14 gallons per person). That gives each person 2 quarts to drink and 2 quarts for washing & cooking.
For some it will be a challenge to store 14 gallons per person, but if you have room for more it would be wise to store more. The average household uses about 70 gallons a day, which includes laundry, dishes, etc. For a short, local emergency you may not need all of your supply, but your neighbors & friends might need some.