If it's on the driver's side only and begins near the accelerator and the center panel, it's coolant. Coolant can become dirty over time and if not changed. If it is coolant, it could either be a faulty heater core or heater intake valve, which is located in the center dash, or simply a torn coolant hose attached to these parts. Your "COOLANT" light should have turned on on your CHECK panel long before you noticed this leak, and your temp gauge should go up when the car is operating. Coolant steam typically fogs up your interior as an early sign before coolant begins to leak in this area.
Word of advice: if you can't do it yourself, do not trust anyone other than a BMW certified tech for this kind of job. Anyone else will cost you more money and could easily damage it further because they don't know what they're doing.