A man has become stranded at an oasis in the middle of a desert. He knows that it's a six day journey from this oasis to the edge of the desert. He has plenty of empty water bottles with him (and he can fill the bottles with water from the oasis), but he can only carry enough full bottles to last him for four days. [added] The man knows how far he can walk in a day. He's an experienced traveller, and can keep track of how far he's walked.
How can he cross the desert? How long will it take? If there's more than one solution, what's the shortest time to cross?
Answers in spoiler tags please.
As usual in this sort of puzzle, I'm not looking for answers like "He catches a camel as it comes to drink at the oasis" or "He manages on a 2/3 water ration for six days". Don't treat it like a real scenario, but like the artificial puzzle that it appears to be.
Adapted from a puzzle I found here:
http://www.johnpratt.com/items/puzzl...c_puzzles.html