Shut off the water at the main, and see if any water leaks past it.
If not, check the meter to see if the dial is moving. If so, it's between the meter and the shutoff.
You can patch the line, and in some cases, they be all that's needed.
If the line is galvanized, then you may want to replace it anyway.
: I have a major leak somewhere (meter reading was 439 units when read yesterday. BUT--no leaks showing under house, at outdor spickets--no running water sound except at main shut-off valve. I can't find any other shut-offs at the house. I did locate one pressure regulator. Can I use it as a cut-off to see if leak is before the hosue? Will there be more than one regulator? I'm ready to dig buty have no idea where to start. Advise, warnings, etc. will be grteatly appreciated.