Future safety tip, don't take your coolant cap off when the engine is hot! That "escaping air" is very high pressure steam, which is well over the 100 degree Celsius boiling point of water, as when a liquid is under greater pressure it boils at a much higher temperature. If that makes contact with your skin, you'll literally melt your hand.
As has been said, if it's a slow leek over a few weeks then traces of it being left are going to be slight, if any. I would probably go back to the dealer that fitted the water pump, explain that you're not happy and you suspect the water pump has been fitted incorrectly and see if they'll look at it or replace it again.