Nobody, since it is not their problem once the water passes through the water meter. If the plumber was only able to tell you that the leak is after the water meter, you did not have a very good plumber. A good plumber would have been able to tell you if the line to the house is leaking, if the toilets needed repair, or if you had a broken hot water line under the floor, (the most likely problem), or whatever other item was causing the leak.