To determine if you have a sprinkler leak, follow the procedures in “Locating and fixing leaks in your yard“. If when you turn off the sprinklers the meter stops spinning, then the leak is on the pressure side of the sprinklers.
If the meter never spins but you have water showing up in the yard, this would indicate that you have a leak on the non-pressure side. (The pressure side is the side that always has pressure. The non-pressure side is the side that only has pressure when the sprinklers are running.) For pressure leaks follow the same process as in “Locating and fixing leaks in your yard“.
For non-pressure leaks, turn on the zones, one at a time and look for leaks. The sprinkler pipes are only 8-12” deep so they will show up easily with a bubbling in the grass. When you locate the bubbling, dig it up.
Sprinklers are PVC pipe and only have pressure when running. PVC is very easy to repair. In a perfect world the sprinkler company would run the pressure side with a higher quality pipe such as copper,pex or quest.
Fixing it is the cheapest way to do it, but replacing it will ensure that you will not have any problems in the future. Replacing the pipes is a big job but worth it in the long run. If you choose to replace your sprinklers pipes you will start digging at the green box and follow the pipe and all branch lines until they hit the electric controls. After you have located every section, simply uncover every span and replace with your higher quality pipe.