Water is the most important item to store.
A good estimate is to store one gallon of water per person per day for a seven-day period.
A three-week supply is ideal. For example, a family of six would need to store 42 gallons of water for a week's supply (126 gallons for three weeks).
Water is not only used for consumption; it is used for hygiene and cooking purposes, as well.
Following are a few things to remember when storing water:
Do not store any plastic water container directly on concrete as the concrete will leak chemicals into the water and will contaminate it. Concrete also degrades plastic and will cause the container to fail.
Be sure to sanitize the water container and to treat the water you are storing. Old bleach bottles clearly marked make good water storage containers.
Five-gallon bottles that are still factory sealed are good for an indefinite amount of time.Rotate your water supply every six months.
Sources: Los Angeles County Fire Department, Federal Emergency Management Agency