How To Find A Water Leak Outside Underground. Call in a professional plumbing technician. However, just because the leak may be underground, that does not mean you or a professional are unable to locate and fix it.
In most cases, the leak indicator is a small triangle (could be red, blue or white). After you've shut this off, check the water meter to see if the leak indicator or the sweep hand are moving which would indicate that water is still going through the meter. One way to find out is to isolate your sprinkler line from your house line.
The sounds leaking water makes in a water line are the key to finding an underground leak.
When the pressurized gas finds a leak, it comes blowing out, producing a loud hiss. Thankfully, you don’t have to be a professional plumber to confirm if you have a water leak underground. After you've shut this off, check the water meter to see if the leak indicator or the sweep hand are moving which would indicate that water is still going through the meter. Of course, the easiest way to find the source of a leak is to have a plumber find it for you.