I need to dig a trench about 20" deep across my yard, which has underground sprinkler system, installed 3 yr ago. Sod was then laid. Is there a way to determine where the interconnecting water supply goes from head to head? I hate to dig away & then have to go back & repair several lines. All other utility lines are located & marked. Rob in Wichita, KS

I have a wire locator by Progressive Electronics I would use, or any others.
If I am following an empty water or electric pipe, I push a fish tape through, attach signal and follow the Null.
Sprinklers and the tubing and 90's may be impossible, unless you maybe pushed a very small wire with a head attached, pushed by water pressure.

I was thinking you may be able to use water pressure to push a small wire from start to a sprinkler head. Maybe cap all heads off and with water pressure push water, or use a vacuum? 90's make it tough.
I have heard of a locator that works on empty pipes, will see if I can locate.

Try this page, toward the bottom for the
"Thumper" and the "Knocker".:
PVC plasitc pipe locators (http://www.rjmcompany.com/Plastic-Pipe-Locator.htm)
Ground Penetrating Radar is also shown, may not be an option, Are you a Lottery winner?