An emergency water plan should have two layers: a dependable supply stored before a disruption, and a documented way to treat an appropriate backup freshwater source if stored water runs low.
The CDC recommends storing at least one gallon of water per person per day for a minimum of three days. When space and resources allow, households should try to maintain a two-week supply. More water may be needed for pets, medical needs, pregnancy, hot climates, or physically demanding conditions.