My house is on solid slab and is 2 story with bathrooms upstairs. I need to locate where 3/4" water supply line(s) are located inside existing downstairs interior house walls, or at least roughly locating, before cutting into wall to specifically locate the line. Reason being that I need to run a new water line from this supply and code won't allow tapping to 1/2" lines. Can't do it from where the only known 3/4" line is at my water heater downstairs. The supply line I'm seeking would definitely be in a downstairs interior wall (not exterior) running upward to baths. Any suggestions on how to approach finding the line?