[Zeke]

Monitor your meter when you know there is no water being used in the house and elsewhere. It will be over hours rather than minutes, so you have to know your toilets, irrigation and faucets aren't dripping.

It could be ground water (you hope). If not, you can run a new supply where there is no paving. Or, you can circumvent the area with a new supply that doesn't go all the way (temporary solution).