Without seeing the coolant actually drip from the water pump weep hole, there is no way to know where it came from.

That plastic pan catches everything, and a coolant leak anywhere from any hose ends up in that place.

Since you are taking your car to the dealer, I'd have them investigate the problem.

It can lead to a catastrophic problem if you are losing that much coolant for the light to come on.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".