Open your water meter box and look at the meter readout. Dial or Digital – it depends on your city.
On a dial type (looks like a clock) look for movement on a small wagon wheel or triangle shaped movement within the dial. If you see rotational movement, you have a leak somewhere in the water system.
On a digital water meter, look for a flashing arrow (or in League City a plus sign inside a circle), just below the number read out. If you see either of these two symbols you have a leak in your water system.