If you've just got the car, also check the housing where the HVAC lives (big black box behind the dash in front of the gearstick). This is the source of the water you see under the car, but on some Foci (mine included) not all of it gets out, the remainder ending up on your passenger footwell carpet! To avoid confusion with the windscreen scuttle leak which also ends up with water in the same place, make sure you look for it on a really hot day, when you know the car is dry and peel back the floor carpet for a better view.