Remove the wiper cowl. Clean it all out and inspect it for things like missing or poorly applied seam sealer. It might be that if a gap was left in the seam, it might not have mattered, but as debris builds the water is leaking in.
Windscreen seal might have been compromised.
AC drain might be blocked. Get under the car and above the transmission is the little tube it drains from. Use a coat hanger wire or narrow plastic to carefully clear it. Squirt some water into it and flush it a little.
If the heater core has let go, you’ll have coolant in the cab, not water.
Remove the door trim, inspect the plastic weather/dust sheet is intact and sealed all around. Water comes through a perished weather strip on the door, down the inside of the door, onto the trim, down into the footwell.