Stocking water reserves should be among your top priorities in preparing for an emergency. You should store at least a three-day supply of water for each member of your family. Everyone's needs will differ, depending upon age, physical condition, activity, diet and time of year.
A normally active person needs to drink at least two quarts of water each day, but the heat of summer can cause a person to need double that amount. Children, nursing mothers and ill people will also need more. You will need additional water for food preparation and hygiene, so it is recommended that you store a total of at least one gallon per person, per day.