You'll have to check for a leak (external or internal through engine)... VW Coolant usually leaves a stain (dry pink powder) that you can spot and
follow back to its source.

Don't forget to check the inside of the vehicle (front carpets) to rule out a leaky heater core under the dash.

If you are 100% sure there are no external leaks, have the head gasket checked at a VW Shop.... coolant in the exhaust usually shows-up as white smoke
or steam.... but with colder climates now, white steam (condensation) can be considered normal, especially when first starting the engine.

Common leaks on TDi engines:

- water pump (coolant dripping from behind crankshaft pulley)
- thermostat flange or r-ring seal from pipe that mounts to the side of the same flange
- radiator
- plastic coolant flanges at heater core fittings (at the firewall)
- reservoir cap not holding pressure
- heater core inside the vehicle

Take a close look around to see if you spot anything, once you do, post a picture here.

Thomas