Now that you have decided how much water to store, how do you store it and how long is its shelf life. In theory if you put clean drinking water into a sterile container it should store indefinitely. In reality it is hard to meet these requirements. The method, I use is to put tap water into clean containers (I am on a municipal water system). I then add a small amount of chlorox, 16 drops per gallon as a safety measure. I then seal the container. I know the chlorox will only last from 6 months to a year, but it will destroy any bacteria in the container and as long as it is sealed from contamination the water should be good.
The types of containers you can use vary greatly. Suggestions include 2 liter soda bottles, they are tough and will last almost indefinitely. Some juice contains are excellent. Stay away from plastic milk bottles, they break down over time and will leak. Military five gallon cans are a good choice. One advantage to them is that they have a strong handle. If you have to carry water some distance you can run a piece of wood or metal through the handle and two of you can share the load.
Fifty five gallon barrels are good, but make sure they are food grade and have not been used for other purposes. The disadvantage of fifty five gallon barrels is that they are hard to move. There are many good choices for larger containers including the 275 gallon cubes and the 2500 gallon irrigation tanks. I know people who have connected these larger tanks into their water system to rotate the water. The only disadvantage to this is that if the water system becomes contaminated it can affect you.
Where to store water, I know a gentleman who fills every 2 litter soda bottle he can get his hands on and throws them into the crawl space under his house. Storage is often only limited by your imagination. If you have a water bed and intend to use it for water storage, be careful of the chemicals, they add to prevent mold and algae. If your container will be exposed to light, a dark container is better. This will prevent the growth of algae in the container.
Always have a good backup plan to filter or purify your water in case your water becomes contaminated. There have been several posts on purifying water on this site. You can find them by clicking on water purification in the categories section or by doing a search on this site. In the future I will post more on water.