Advice Need, Water coming in from behind the dash, vent stuck open?

[Advrider]

I had a new windshield put in last summer and ever since I've had a leak (only when washing it, not when it's raining etc.) the water comes in behind the dash somewhere and I know it's not from the windshield, I had it glued in but i do think the first guys who tried putting in the new windscreen did something and I'm not sure what. I think there must be a vent that is stuck open to allow water to come into the cabin and I can't figure out where it (the vent) is or how to close it.
Sorry in advance if this is a stupid question, but help/advice is needed.
Thanks
Advrider

[darthracing]

How did you find the leak/notice it?

I found a puddle in my passenger footwell today whilst vacuuming - I too had a windshield replaced last year, but can't figure out where the water is coming from...