Underground leak detection cost usually runs about $150 to $600 to locate a hidden line, according to third-party cost guides, before any repair. The figure depends on the method used, how deep the pipe sits, whether it runs under a slab or across the yard, how easy the access is, and whether repair is bundled in.
The method does most of the work on price. A plumber may start with a pressure test or listen for the leak with acoustic equipment, then confirm the spot with thermal imaging or a camera inspection. Simple single-area checks sit at the low end of the range; a full-house search that combines several methods lands higher. Industry cost guides put locating a hidden or underground leak at roughly $150 to $600 before any repair, and This Old House reports the same band for slab leak detection.
Depth and access push the number up or down. A leak a few feet down in soft soil is quicker to pin than one under a concrete slab, below a driveway, or along a long run to the meter. Jobs that need specialized equipment to avoid tearing up the property cost more. Where the leak sits also decides how much digging the later repair takes, which is a separate cost.
Most of these figures cover detection only. Finding the leak and fixing it are priced separately, so a quote for the search will not include the repair unless it says so. For how the methods work and what they find, see the underground water leak detection guide and the water leak detection service page. The honest limit on any published range is that it is a third-party estimate, not a quote; the real price depends on an on-site look at the pipe and the access.