Locate plastic water lines
Locating water lines without tracer wire is almost impossible. Your best solutions are Ground Penetrating Radar that start over $16,000 or using an acoustical method.
Acoustical locating involves using sound traveling on or inside the pipe. The sound is applied by a transonde at a hydrant or spigot. It can then be followed using an ultra-sensitive microphone tuned into the frequency range produced by the transonde. This has been proven to be the most accurate and economical method at just over $6000.