Tracing Plastic Water Pipe Underground.
Lawn Sprinkler systems usually have plastic pipe a few inches underground. No metal. :. Can't find it with metal detector.
AC wires can be tracked through walls by the electromagnetic flux around them. Stud sensors today also have a circuit for AC wiring. Could something like that be used? Although city water has some minerals in it, does it have enough to conduct electricity well enough for an electric pulse sensor? If the water in the system was temporarily made salty enough for an EM signal to be traced, would it mess up the lawn once you dumped that salty h2o? Whata bout conductivity of a fertilizer mix?
Medical scans- barium- mildly radioactive. mmmm.... yeah. right.
Chemical sniffers- sniff out those semi-soft pipes? Like dogs sniffing out contraband in the airport...
Use water flow to carry a fine wire through the pipe, then track an EM signal in that wire.
sonic imaging (or at least detection- like the stud sensor)
ground penetrating radar...
That's all I can think of. Every option I can think of has issues. Is there any precedent for something that works in this situation?