Water and acne

From time to time I suffer a bout of the acne, which mostly occurs when I slack off on my water consumption. When I drink a good amount of water a day (6-8 cups) it normally goes away, and when I stop drinking water it has a tendency to come back (or at least stick around longer).

My question is, why does drinking more water help get rid of acne?

Dry skin causes/promotes acne. Dehydration leads to dry skin.

A cite.