Found out I have a water leak when received water bill. Put in a new line this summer and new regulator. Regulator box has water in it, should this ever happen?

If the box isn't completely sealed it may get ground or rain water in it.

By "regulator box" do you mean water meter enclosure? Yes, This could be rain wate Have you gone out and felt the connections for a pressure leak? Has the water drained away yet? Let me know, Tom