Four Things You Need to Survive a Long-Term Crisis: Water
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"A gallon a day will help you stay hydrated and prepare food. If you have all dehydrated food and you want to wash up, you'll need more. The average person has a 50-gallon hot-water heater at their house. If the power goes out, you can turn that off and drain the water from it – that's a lot of water people have access to."