[pdurrant]

Originally Posted by omk3

Spoiler:

Take water for 4 days, leave the oasis.
After 1 day, leave water for 2 days in a safe place, use the remaining water to get back to the oasis. (2 days have passed)

Take water for 4 days, leave the oasis again.
After 1 day, you are left with 3 days' water, but find the 2 day's water you left (I hope no one stole it), so you have water for 5 days. (3 days have passed)

Go on for one more day (distance of two days). You have now water for 4 days. Hide water for 2 days there, use the rest of it to go back to the oasis. (6 days have passed)

Almost right. At one point (the fourth day) you're trying to carry water for 5 days. You can only carry enough water for 4 days.