Leak outside firewall by heater

[Best]

I have a 2006 3500 an have a leak out of a small rubber hose outside of the fire wall just under where the heater is. What is this drain hose for? It looks like clear water & not anti freeze. Does this drain from under the windshield vent area? I don't think its a bad heater core. This is the 1st time I have seen it leak. Has anyone else had this happen?

 

[Hoefler]

Condensation drain for the A/C. Blowing snow and any rain that makes it way into the heater box will also drain there.