I have no dispute with 64 oz being about the required water, but the source of this is in dispute.
The earliest source of 64 oz per day I have seen is from the US civil war, how big should a standard canteen be? The decision was two quarts was the minimum that a cavalry or infintery could get by for a day on, so that was the canteen size selected. Nothing but experience, no science.
This is not much different from the Greek goatleg of water from 2000 plus years ago.
So 8x8 is not a modern concept, but something that is about right, as demonstrated over time. Many of us overweight people run a bit dehydrated, so to drink more water is not out of line recommendation. A big glass of cold water does tend to force an end to a meal.