Finding the source of a slab leak can be a challenging task, but there are several methods that can be used. One common method involves using specialized equipment to detect the sound of water flowing through the pipes. Another method is to use thermal imaging technology to locate hot spots caused by water leakage. Additionally, a plumber may perform a visual inspection of the plumbing system to look for signs of water damage or corrosion. It's important to hire a licensed and experienced plumber to ensure accurate detection and proper repair of slab leaks.