Principles of a Hookah

Dear Forum Users,

Please look at this diagram:

http://kronicunderground.com/wp-cont...1275695035.png

I know that when you suck in on the hose you create a pressure difference which pushes the air from one end, through the water, and into your mouth/lungs finally.

Can anybody help me making a mathematical description for this system?
Or tell me which equations I can use to describe the Hookah.