If I might add a few items to the discussion. There are a number of underlying ideas in the drawing of the pentagram which on the surface appear to be confusing. In the larger context there is a well defined logic that allows intent to be reinforced through understanding. Below is an image of the pentagram in question.
(IMG:
http://www.sacred-magick.org/uploads/1171108599/gallery_104_25_1048.jpg)
We can see that the motions are the same for the Banishing Air and Invoking Water Pentagram.
The question is Why?
The answer is shown within the relationship of the two elements (Air/Water). They are opposing elements in both direction and nature.
Air is an active element in the East.
Water is a passive element in the West.
Think of how these two elements face each other at opposite ends of the spectrum while you are in the circle. The act of banishing Air creates much the same result as Invoking Water and vice versa.
This provides us with a number of options. If one feels an overabundance of the element of Air we in fact have Two options to balance ourselves. We may:
1. Face East and banish Air. Thus dispersing the abundance.
2. We may face West and Invoke Water. Thus creating an added presence of Water to counteract and Balance the abundance of Air.
Hope this helps to explain the idea.