Water in the footroom under the front seats at C70 I

Good day, dear Volvo connoisseurs, I bought a nice C70 T5, year 1998. A car that I always wanted. Now I have invested a lot without looking at the Euro, but one thing makes me crazy: Water is always standing in the footroom. Somewhere in the rain water comes into the car and that is not too scarce. The sunroof seems to be tight, at least when I drive the car nothing comes in, even when I drive in the rain, But when the car is standing, water seems to enter somewhere. The seats are dry, the amature board also, only in the footroom under the front seats to the rear seats. What can that be? I would be very grateful for tips. LG hjm