The survival rule of thumb is:
3 hours without shelter, 3 days without water, 3 weeks without food.
Ready America says
“Get a Kit”
You may need to survive on your own after an emergency. This means having your own food, water, and other supplies in sufficient quantity to last for at least three days. Local officials and relief workers will be on the scene after a disaster, but they cannot reach everyone immediately. You could get help in hours, or it might take days. In addition, basic services such as electricity, gas, water, sewage treatment, and telephones may be cut off for days, or even a week or longer.
Are you worried about disaster? You can get prepared — especially with safe water. We have selected a very interesting, large inventory of products for disaster prevention and relief, including water purification tablets and systems.