Photo courtesy of Aerofrog
I had the same problem after it had been at the factory for a service last year. The water coolant sensor fixed on the hose was not properly sealed. We were loosing about 1/4 of a litre per trip after the car had cooled and therefore like you found a pool of liquid under the car the next day. It took 2 more trips back to the factory before it was finally fixed. This might be your problem.
