Can anyone advise how water is getting into the Drivers footwell of my Fiat Marea?

Hi,

first you have to determine whether it is engine coolant on your floor, or just water.

Engine coolant has a distinctive, bittersweet taste, but don't swallow it as it's poisonous. If it's engine coolant, I would check the heat exchanger in the air-conditioner assembly. When leakage occurs here, it usually shows on the floors inside the car.

If it's just water I would check the gasket around the windshield, the gaskets around the door etc., as well as underneath the car to inspect for holes or other penetrating damage.