Since time immemorial, if there is one thing that mankind has been afraid of; it has been the coming of the Day of the Doom. People everywhere have always spoken about being prepared for it and have actually gone to great lengths to ration and save for such a day.
But in present times, when the cost of living has been increasing every moment, it would actually be hard for even a single person to survive for too long without the modern amenities. But let us suppose someone does manage to escape doomsday and has been left alone to survive, he would actually need quite a lot of things to simply stay alive.
One of the major requirements during such times ofcourse, would be water. And it has been calculated that since a man need about 15 bottle of drinking water alone which goes up to 200 gallons a year if he were to survive.
They would have to grow their own food and also learn skills of survival that will help him survive in such a condition. It might not seem as hard but when you count all the practicalities, it is actually a scary when you think of such a scenario.