Without drinking water, we will die within 3 to 4 days.

World Health Organization (WHO) studies indicate that we need 5.3 gallons (20 liters) of water per person per day for survival, and 18.5 gallons (70 liters) per person for medium-term recovery from a disaster.

The technical notes explaining this information, as well as other useful notes about water, sanitation, and hygiene (WASH) are available here.

The notes are relevant to a wide range of emergency situations, including both natural and conflict-induced disasters. They are suitable for field technicians, engineers and hygiene promoters, as well as staff from agency headquarters.

WHO - Water for Emergencies