To check for leaks:
Turn off all the sinks, dishwashers, ice makers, irrigation systems and other water-using devices in your home.
Then, check the leak detector triangle on your water meter. If it's spinning after everything is turned off, you probably have a leak somewhere!
If you do detect a leak, check to see if it's your toilet by adding a few drops of food coloring to the water inside the tank. Wait a few minutes. If the water inside the bowl changes colors, then you've got a leak. Simply replacing the rubber flapper valve inside the tank can often fix leaks like these.