Orlando Sentinel Article:

Windermere couple discover that their copper pipes in slab were leaking.

The problem turned out to be a slab leak. One of the home's copper pipes embedded in the concrete foundation apparently had sprung a leak. A plumber spent 8 hours and $400 of the couple's money but failed to pinpoint the leak. The home owners turned to a leak detection company. A technician with the "Leak Doctor" arrived and found the leak in less than 10 minutes. It was a slab leak originating from the water heater.

...by Denice Bates Enos - Special to the Sentinel