I seen this on 1 of those commercial tips on the golf channel and it is a great tip to help hit the ball straighter whether you struggle with a slice or hook.
If you slice place the water bottle just outside and behind the ball and make sure you dont hit the water bottle. The only way to not hit the bottle is to make sure your swing is coming from the inside.
For a hook you put the bottle between you and the ball and make sure you are swinging a little over the top to avoid hitting the bottle. (not 100% sure on this one, haven't tested the anti hook)
I havent tried it yet but i did something similar with a box last summer to help me start swinging from the inside more and it has helped where my misses now are left. If i hit it right it is usually a push with my higher irons (8,9, and wedges) which i dont get since my swing feels like its coming from the inside. Maybe i am standing too close...
Anyways i think it is a good tip to get you swinging em' straigher.