Did you have yer windshield replaced anytime ago? Could be a lot of different things. Vent. Grommets.
Yer gonna have to have someone help you by looking fer the leak while someone is running the hose. Be methodical...take yer time. See if you can see spot any water drip tracks before you start. You could dust/blow some corn starch underneath yer driver's side and run the water and see where the tracks lead...
