Ok, first you need to check the interior heater is working properly, and it blows out steady hot air.
If it doesen't, then it is almost definately your heater matrix, leaking coolant into the cabin and onto the floor. Trust me, that's the last thing you want (but a known prob with some MK2 owners).
You could also try and see the colour of the water in the footwells, and make sure it is CLEAR rainwater.
Also check the coolant hoses that go into the dash at the back of the engine bay, and if they don't have a valve fitted to them, then VW themselves might just fix the whole lot 4u, 4 free!
I hope that it is just a minor seal problem leaking rainwater.
Good luck Paulo
Obrigado, H.