If you are in a situation that requires reduction of water, a person requires 1 ml (about 1/5 of a teaspoon) of water for each calorie consumed. Normally a grownup will consume roughly 2000 calories on a healthy lifestyle diet. This means that 1 gallon will last almost 2 days. An average bathtub will hold about 62 gallons, cover the drain and the overflow with plastic wrap and filling it to the top is roughly 110 gallons (200 plus days).

The Life Straw... See the Testimonial. The lifestraw would provide roughly 500 days of drinking water.

I suggest having half a dozen lifestraws (depending upon the size of your family) and rainwater catchment (plus having supply of water on hand) would be sufficient to get through any crisis.