Volvo C30 water leaks?

[csl]

My dad has a 2010 Volvo C30 2ltr diesel and has owned it from new.
He likes the car but it has been problematic in way of water leaking into the drivers foot well following some (not every) rain fall.
It has been back to the dealer 3 times for this to be rectified and they don't know what could be causing this problem.
Any guys on here come across this with this model?

TIA.