The City's water crews repair main breaks and leaks, replace leaking service lines and look into customer complaints about unusually high or low water use. Pipes on your property are a different matter. City Code gives the consumer complete responsibility for installing and maintaining the water facilities on the premises, and says the City is not responsible for damage caused by defects in them. A leak under your slab is a private repair.
About 63% of El Mirage homes went up between 2000 and 2009, so any original supply lines have been under pressure for 17 years or more. The City's irrigation leak tips note that a water leak may surface 10 to 100 feet from its source, which is why a wet spot is not always above the leak. Once the leak is pinpointed, ask whether the repair falls under the City's permit for supply line repair or replacement; the same section of its guide requires a shut-off valve before the line enters the house.