During a random walk around I noticed there's a little hose sticking in the pack inlet valves. It's difficult to see, but apparently it is dissipating a spray of water from the airco back into the pack.

Is this correct and why does it do this on ground?

Not sure about the AirBus, But on the B737, moisture is removed from the conditioned air in the water seperator, and is then sprayed back across the heat exchangers to aid cooling.

I would assume the A320 has a similar function.

Rgds

Same thing with the Airbus, water is sprayed into the inlet before it goes into the heat exchangers. For cooling the warm air