If you are out at sea on a sailboat with no electricity (genuine purist) you might have rigged up a sheet of poly in that shape and got plenty of drinking water. It helps to be sitting over a large body of water. Probably wouldn’t be so effective in an arid inland region of dust and sand.
I watched Survivorman do this very thing.
I remember reading about some pacific island years ago, where this sort of thing was the only source of water. Can’t remember the name.