2003 Seat Leon leaking car

water is ment to leak into the door check the drain holes at the bottom are clear.the most likly problem is the membrain if you remove the door trim there should be a polythene covering if it has a hole in tape it over. later vw derived cars had an ally cover which is also sealed to the door

The problem you seem to have is commom to leons and some toledos of this year. The problem is the seal between the door and the window/lock panel which is under the door trim held in by about twelve 10mm bolt. The is a porus and lets water pass through and leak into the door trim which then runs into the car via the door rubber and over the kick trim filling up the foot well. This can happen to all the doors the signs are a foot well full of water you may see a dribble of water as it runs over the trim. The cure is to replace this seal, Seat use a plasticen type seal on a roll this does cure it. You will also need to seal the speaker as the water can run through it as there is no cover over the back.