Avoid the long lines and bulky packaging associated with bottled water, especially in emergency situations. The average human needs 1 gallon of water to survive for 4 days. This 15-gallon tank could last a family of 4 for just over 2 weeks. When severe weather is predicted, simply take your standard shower head off and replace it with the provided assembly. Water costs $9.60 per gallon on average when consumed in bottled water form. Tap water cost $0.004 per gallon. This unit can be deployed in under 2 minutes by following these 6 easy steps on the backside.