You can survive for many days without food, but only a short time without water. Many kinds of emergencies can cause a loss of water to your home.
Additional water is needed for brushing teeth, bathing, and dishwashing.
Buy one gallon jugs at your market, or store tap water in well-washed soft drink bottles. Clearly mark the bottles with the current date. Store them in a cool, dark place. Use the water and discard the bottle within one year of the storage date. These can be kept for many years in a cool, dark location, as long as the seal remains unbroken.