Bottled water has a long shelf life. It lasts essentially forever, as long as the seal hasn't been broken, though it might not taste great a year or more post-bottling.
Can tap water also be stored indefinitely? Homeland Security recommends households keep at least one gallon of water per person per day for three days in case of an emergency.
While you can use commercially bottled water, you can also store water straight from your kitchen faucet.
The Federal Emergency Management Agency (FEMA) recommends storing tap water in clean plastic, glass, enameled metal, or fiberglass containers. Once you have filled the container, it should be tightly sealed and stored in a dark, cool location.
The water should be rotated out about every six months. It won't necessarily go "bad," but you may get some algae on the container and there is a slight risk of bacterial growth after several months of storage.
It is generally suggested to discard bottled water within two weeks after you open it, but FEMA's recommendation for how long you can keep tap water is quite a lot longer.
If the water starts to turn green, use it to water your plants; then clean the container, and refill it with fresh tap water. Similarly, discard the tap water if it develops any other discoloration or has an "off" odor.