Blue Can Long Term Supply
Most emergency preparedness managers recommend at least half a gallon to a gallon of water per day per person. This is because each person will need about half a gallon of water just for drinking and the other half for sanitation and food preparation.
A case of Blue Can Water is 2.25 gallons of water. So at the bare minimum, a family of four should have at least two gallons of water for drinking alone. The extra quarter gallon could be used for pets, food preparation or sanitation purposes. Also, a family of four might include children or infants whose requirements might not be as high as adult family members.