Part 1 https://www.youtube.com/watch?v=si9iqF5uTFk
I was on a hike that recommended 1 gallon to complete it for 5 miles round trip.
I’m sure there is a method to the madness of 8 gallons per person that isn’t easy to see. There is a lot of rounding up with the military also.
Also you need to clean your home - you don't want to get sick in a catastrophe scenario.